Difference between katana with niku and without niku

There are different types and degrees of niku, got starters. Classically, the entire bevel would be convex all the way to the edge. In modern production, especially on specialized tatami cutters, the bevel is flat. Sometimes the edge itself is convex, while the body of the blade is flat.

Mostly, the degree of niku, or the lack thereof, determines the angle at which the material initially encounters the blade. A thin, flat bevel, theoretically, yields the least resistance. Unfortunately, it is also more easily prone to damage than a more convex bevel.

Sword design is a compromise of these things, being cutting efficiency and damage mitigation. Thinner swords with smaller edge angles will slice more easily through something soft like tatami mats, provided good form by the user. If the cut is off even a little, the thin blade is more liable to bend, or even break, than a thicker blade would be. Especially the wider blades popular in tameshigiri contests. A thicker blade, with a more convex edge, would take a little more effort to go through a target, but would be less likely to bend on a bad cut, or chip if it struck something harder.

Here is a diagram. 
Afaik battle swords had more niku, dedicated matt cutters not. 

Niku is not an on/off switch. It's a matter of degree, or rather amount. You are right that it's a trade-off between durability and cutting performance. But don't forget that with everything being equal, having more niku meaning leaving more material on the blade resulting in more forward heaviness and generally speaking a less nimble sword.

When the blade has more niku, when the blade meets other blades in parry, or bones in cutting, the hardened edge can suffer less severe deformation or chip, which means over time it will less likely result in cracks that eventually cause the blade to break in half.

Antique nihonto generally have niku of different amount. Being re-sharpened or having the damaged edge fixed will increase the amount of niku, not less, as the portion near the edge is removed and then blend into the rest of the edge bevel. Having niku on blade made with tamahagane is a necessity (along with have less distal taper, so the blade on the upper portion is thicker than swords from other cultures) to maintain the durability given the steel quality of Japan, and the differentially hardened blade with very little spring temper. If their blades are to have minimal niku and the same degree of distal taper as let's say Chinese and Korean swords, Japanese swords would have broken a lot more often (which indeed happened once upon a time, until the specific differentially hardening and form of sword became popular and almost codified in Japan).

Having niku on blades has always been an unpopular practice in China and Korea. It has less than nothing to do with the ease of modern reproduction. On double-edged blades with diamond cross section, Chinese smiths have always been trained to make the edge bevel almost straight (which means zero niku). So were the Koreans. Triangular cross section on single-edged swords are most popular in Korea an China.

16th century military and martial treatises from China specifically called out makers forging blades with shoulders and muscle (niku) as unskilled. In earlier times, other cross sections were popular once. Some Chinese swords before the 9th century had shallower bevel and single-edged ones were pentagonal, and double-edged ones were octagonal, but due to very large amount of distal tapering and the concave geometry between the spine and the shoulder, the blades get very thin at the point of percussion so the impact to performance is almost minimal.

Today's reproduction katanas from China (mostly made by apprentices, as making Japanese swords are generally looked down upon once you get the mastersmith certificate) have varying degree of niku. Some forges like to make blades with a lot of niku, others prefer making them with less, or none. It has nothing to do with the ease of production, as grinding some niku is neither more or less difficult than grinding a bevel flat as a mirror, with the degree of automation in their workshops.

No, I don't think Japanese culture is seen as inferior to Chinese in China (antique nihonto and shinsakuto purchased and brought to China are prized). But clearly in the swordmaker culture, which has vivid record date back to 2500 years ago, certified "Artisans" (which is what mastersmiths are called) would definitely be seen as "less serious" if they make non-Chinese swords (not just Japanese swords or European swords) themselves. It has something to do with the preservation of one's own culture, it also has something to do with nationalism and xenophobia. China, like other East Asian countries, has the national ethos that's simultaneously xenophilic and xenophobic.

I think swords almost always command tremendous respect in every culture that has a long swordmaking tradition, say India, Persia, or Europe. Even in the premodern era, swordmaking was still practiced in an almost ritualistic way. With their necessity of being arms gone, they are seen as art and tradition to be treasured. It's only in the 20th century that the most rigorous standards of swordmaking were lost in most countries, as swords were mostly forgotten, not to mention that most cultures with strong swordmaking traditions had become impoverished so they weren't afforded the means to preserve a tradition.

However, the current religious reverence to nihontos is a culmination of pop culture in recent decades, not to mention Japan's commendable post-war effort to revive the tradition as fine art.

Meanwhile, in China, this tradition really never went away, but it had certainly degraded over time. Even in the 19th/20th century, high quality of swords were still made (Ryan Sword's parent company was started in the 19th century in Long Quan, and it's still considered a young player in the local industry), but the functional part was overlooked more and more (still not to the degree of those aluminum floppers--those are circus props) to make place for artistic interpretations. If you look at the Han Dyasnty jian offerings before LK Chen entered the scene, most were just impressionist takes with horribly shaped cylindrical grips and overly heavy fittings. The blades are usually lovingly forged and polished, but the fittings are fitting (no pun intended) to their high-end gift status, without any ergonomics and handling in mind.

You are right that for a long time, the interests in the West about Chinese swords were low, so most websites oriented towards overseas buyers don't even bother listing their higher-end swords, which are almost exclusively Chinese. Jian and occasionally Dao are high-end collector items. Those made by the national-level smiths are sold for considerable sums--often hundreds of thousands of dollars. You will never see these listed on the English websites because these are only for their low-end stuff (almost exclusively Japanese style swords and occasionally medieval European as well) typically sold through subsidiaries specifically set up for this kind of business, to distance these offerings from the mastersmiths who are the owners that run the parent company. Those mastersmiths themselves can occasionally dabble in higher-end katanas usually with san-mai laminate construction, but even these are among the lowest end of their own offerings.

Things are starting to change though. People like LK Chen emphasize on historical authenticity and do adequate research on antique examples usually excavated, in similar ways to how Peter Johnsson does research for Albion designs. His design and marketing are targeting primarily the Western market. More professional websites have been set up for this offerings, usually with extensive introductions to Chinese history and culture. LK Chen shows that the original Chinese swords--even the steel ones dated back 2400 years--were ahead of their times in terms of durability and lethality, with otherworldly weight/size ratio, spring temper and refined blade geometries that make them more than functional.

I don't think many in the Chinese swordmaking scene have done that by studying the antique originals (not even Hanwei) and military treatises that sometimes include passages talking about the specific requirements to commission swords with details weight/size ratio, blade geometry and distal/profile tapering to equip the commander's regiment. Today more people are doing test cuttings and drills with functional swords like LK Chen's.

Going back to Nihonto. For the longest time, Nihonto were indistinguishable from Chinese and Korean swords, because that was perceived in Japan as how swords should be properly made. They brought back swords from China and Korea, sometimes through mercantile activities, sometimes from overseas military campaigns (to assist their allies in the Korean dynastic struggles, for example). They studies them, and tried to replicate them. They kept making it this way and their swords kept breaking, until they had noticed the error of trying to replicate swords from neighboring cultures, given their poor native iron source--the satetsu (yeah I know there are higher quality iron cakes and imported steel but those were most prevalent in later centuries). Japanese had to use a far more laborious process to produce steel that's on par with steels from other cultures in terms of impurities and inclusions. They had to codify (more or less) the differentially hardening process (similar processes were used in other cultures as well, of course), and focused on primarily single-edge swords to ditch the older continental style double-edged swords. They had to make the upper portion of the blade thicker compared to any other swordmaking cultures. All these, are to ensure the durability.

If we go back to the topic--the niku. It's not unique to Japanese swords, nor does it make them superior. It's just a convex geometry along the edge bevel. If you look at medieval European swords up until the early 14th century, they all have rather pronounced convex geometry with a signature lenticular cross section (hence very pronounced niku). But near the point of percussion, where you cut with the most, it's a lot more thinner than Japanese swords. Take a late 13th century grete swerde of war, and compare to a Koto style uchigatana from the same time period, or let's be more fair in terms of size, an odachi. The European grete swerde is usually only half as thick on the upper portion as the Japanese one. But they are a lot broader and have noticeable spring in the blade, so they are less prone to taking a set. Japanese swords however have a tendency to bend, but less likely to break (compared to a thinner sword like the continental Asian sword made with Japanese steel), due to having less distal taper to remain thick throughout and the differentially hardened blades.

This definitely is ingenious. As if you are 10 meters behind everybody at the starting line, but still finish mostly on par with everyone else, you must be doing something right. But it does have some drawback, and that is to its handling. I don't want to speak for ALL Japanese swords, but on average having less distal taper (and generally less profile taper, too) makes them more like a bar, and less maneuverable compared to swords from other cultures. All the JMA practitioners would be up in arms protesting that "we do declare nihontos are very nimble and agile"!

I'm not denying that, but it's mostly due to its size and proportions. Anyone ever wonders why an average size katana used predominantly with two hands has a shorter blade than even the average Chinese/Korea/Indian/Persian/Arabic/Turkish/European swords used predominantly with one hand? Well it's because of its handling characteristics. Some attribute it to the average height of Japanese people in this or that period. It may have something to do with it, but then it can't explain away why the grip is far longer on the average katana than even the average European longsword which is also used predominantly in two hands, but also can be used in one hand in certain situations (grappling, riding, picking up a shield occasionally with the offhand). The longer grip on the average katana is there to maximize the leverage and perhaps sometimes enable a longer and thicker tang to balance out the blade. So the size and proportion are what they are on a katana to ensure its maneuverability. I know that koto style Japanese swords tend to have a bit more distal taper, but still not by much. If you compare an average nodachi with a 36" blade with a medieval European longsword with a 36" blade, I guarantee you the nodachi is always slower moving and harder to redirect.

Very, most old Japanese have a pretty decent amount of niku. It’s important since it makes edge loss far less likely.

The exceptions such as Yamato and nanbomucho that had little niku instead still used tricks like wide shinogi or utsuri to boost the odds of a blade surviving.

You want it. Niku means the edge can tank hits. The only detriment is it might mean slightly less sharpness but it still helps when cutting thick targets.

Lots of misconceptions, have to address them one by one.
Literally the first sentence of the article that you linked states that Japanese swords got their signature curvature in the 9th-10th century, but concrete evidences only come from the 11th and 12th century. That's not the time of the Roman Empire's division (late 4th century). It's more of the time of the first three crusades, which is more than seven centuries after the capital moved from Rome to Constantinople hence the name Eastern Roman Empire, and six centuries after the fall of the Western Roman Empire.

Prior to the unique curvature, Japanese were largely using chokuto, and tsurugi, and yes these were completely indistinguishable from the continental East Asian swords, because they were Chinese/Korean swords brought back to Japan, or swords of the same style made in Japan. The word Tachi (大刀, notice: even though it pronuces similar to the tachi called in later centuries, it's not the same word, later tachi is actually the characters 太刀 meaning "grand sabre", they happen to pronounce similarly) at the time literally just meant "big single-edged sword". In fact, continental-style single-edged swords were called Tachi (大刀). Many original Chinese-made swords brought back to Japan and housed in treasure houses at temples are called Tachi by Japanese, specifically tara-tachi, meaning "big single-edged sword made in Tang Dynasty (China)". One of the most exquisite examples is the tara-tachi housed at Shōsōin Repository of Tōdai-ji Temple in Nara, Japan. It is confirmed to be a purchase from Tang Dynasty (618 to 907 AD) China and brought back to Japan. Today it is one of the national treasures of Japan.

In fact, most Jōkotō (ancient swords) in Japan are either replicating Chinese/Korean swords either in Ring-pommel style, or the pommel cap style straight single-edged swords.  Let us take a look at the comparison of two Chinese-made Dao above, and one Japanese-made Jōkotō, done by Metropolitan Museum.


A minority of the tachi (大刀) were taking inspiration from the swords of the Northern Emishi people (called the "shrimp-barbarians" by the Imperial Japanese), called the "fern-head pommel sword". If we take a look at a collection of Japanese-made Jōkotō, we can see the majority are older-Chinese-style ring-pommel sabres or the Tang-Dynasty-style sabres with pommel caps, and the a minority is the fern-head pommel style taken from the Emishi northern barbarians. No curved swords were spotted, because the heat treat process that produced the unique curvature hadn't been used by this time.


Here we can see different styles of Jōkotō tachi, note tachi is written as 大刀，not 太刀.

So it is 100% historical to say that Japanese swords for millennia had been Chinese/Korean swords (those two actually were indistinguishable anyway at the time) in make or style, until Japanese swordsmith refined their process to produce the unique curve, but it's not just the curvature, which is just a by-product of the heat treat process. Just because you see the English word "tachi" used in the context of Jōkotō, doesn't mean it's a 14th century style tachi. In English they are translated into the same word, because they sound similar, but they are not even the same word as 大刀 isn't the same as 太刀. I don't know whether you can read kanji (BTW it means "Chinese characters"), my gut feeling is you can't. It would be useful to pick up some understanding of kanji if you are to read literature on Nihonto.

Like I discussed before, having less distal taper on the blade is a unique trait on Japanese swords. It is not seen on swords from other cultures (not to this degree). Along with niku (which is not unique to Japanese swords at all), the lesser degree of distal taper than swords from other culture is to ensure durability of the blade. I did also state Kotō style Japanese swords (up until the 16th century) tend to have more distal taper than swords made in recent centuries, therefore slightly livelier in handling, but I knew it was too much to expect people to read.

The Kogarasu-maru (at least the one in the Imperial Collection) is almost certainly a Kotō style style, not a Jōkotō. It is definitely NOT made in the 8th century by 天國安綱, who is a mythological figure rather than an actual person. A person by that name might have existed, but the deeds in the legends are stories by much later periods, likely based on many different historical figures, and possible many urban legends as well. It's like the Kusanagi no Tsurugi among the Imperial Regalia IS NOT a sword discovered in the belly of an eight-headed serpent by the God Susanoo. You can't interpret a mythological story literally. It doesn't work like that, even if they tell you there's this actual object inside a box.

There is no evidence that the current Kogarasu-maru is the original "Kogarasu-maru" sword mentioned in the Tsurugi no Maki ("The Scroll of Swords", note the usage of the word "tsurugi" which denotes "double-edged straight swords" exclusively) mentioning it as early as the 10th century, as an heirloom at the time, and therefore likely be a tsurugi (double-edged straight sword), not the stereotypical Kogarasu-Zukuri katana with a false edge we see today.

Look, I didn't read this paper as it's paywalled. I don't want to misrepresent their arguments and findings, but I doubt they claimed "Tamahagane" is "remarkably free of impurities or edge inclusions". The inclusion and impurities is what makes it steel. Carbon is impurity, if it's "free of impurities", it means there's no carbon in it. Carbon is what makes steel hardenable. Free of carbon, it's just a lump of iron, it can't be hardened, it's not gonna be made into sword blades. Other includions like the Manganese are there to introduce different properties into the steel, like hardenability, corrosion resistance, shock resistance, etc. It's not the existence of impurities and inclusions that's the issue, it's the specific content, and how evenly they are distributed.

Nanban steel importation is a FAR later phenomenon, than the time when Japanese swordsmith needed to innovate to produce higher quality steel called tamahagane and use differentially hardening process (late-Heian period). So the supposed steel quality of "Nanban steel" is completely irrelevant. Even if we are to discuss the Nanban steel import, although "Nanban" means "southern barbarian" which denotes to Europeans, the steels imported by them were for the most part not European steels, but from neighboring cultures, and because of the mercantile nature, some of the import was of bad quality, others was of good quality. Kozan Sakakibara had commented that the Nanban imported steel was great for swords. It is of no consequence, one batch of import might share no common trait to another.

People in the 18th century cannot possible break down the steel to understand its chemical composition, let alone having a manufacturer chart for heat treat recommendations. To benefit from the actual quality of the steel, one has to understand and yet better--be very familiar with its heat treat process. It is entirely possible that native Japanese smiths were simply not well acquainted to these steels, unlike the steels they work on day in day out. You can have the best super steel even today, and completely ruin it if you are not familiar with it, let alone back several hundred years ago.

Also in the summary of that paper, nowhere does it mention Japanese tamahagane is free of "remarkably free of impurities or edge inclusions" like you said, but it does mention Japanese sword blade has very fine grain structure. First of all, nobody says antique Nihonto has coarse grain structure, so I don't know what you quote this paper for. Secondly, how many antique swords did they break in half to look at the cross sections to examine the grain structure? Not many, my educated guess. Did they compare it to swords of the same period from other cultures? If not, why do you even assume it is of finer grain structure? Not to mention, their steel tempering and design philosophies are completely different, which is exactly MY POINT.

The summary also states the edge of said Nihonto is hard and the it transitions to a soft spine. Yeah, differentially hardening. Anything we don't know ALREADY?


Well my sentence was cut in half and it sounds different suddenly. What I actually said there was "If you compare an average nodachi with a 36" blade with a medieval European longsword with a 36" blade, I guarantee you the nodachi is always slower moving and harder to redirect." What's the nagasa of your Yamato tachi? Somehow I doubt it's 36".

Here are also what stated in that post:

- the average Japanese sword is made shorter in the blade, longer in the grip to be maneuverable. It can still be nimble enough when the blade on a two-handed Japanese sword is shorter than an average one-handed sword blade from Chinese/Korea/Indian/Persian/Arabic/Turkish/European origins. The grip on Japanese swords, on the other hand, is far longer to utilize leverage to use the not-so-lively blade, but also enables an usually longer and thicker and broader tang to provide a bit more counter balance to a blade that doesn't have a lot of distal taper or profile taper.

- Once again, Koto (10-16th century) style Nihonto tend to have more distal taper than later period katana, which makes them on average livelier.

These are what I stated in the original post, I have to bring up these points again.

Why do you automatically go to "how many antique tachi have you owned and used frequently enough to know the feel"? Did I compare a 14th century original tachi with a shinsakuto made in 2010? My comparison is how a 14th century nodachi with 36" blade to a 14th century medieval longsword with 36" blade. A longsword like these shown down below. If we are to use your logic, "how many antique medieval longswords have you owned and used frequently enough to know the feel"? How many antique Chinese swords, Indian swords, Persian swords, Turkish swords have you owned and handle with high frequency? My guess is, not very many. Well, you don't need to, we have been to museums and collections, people have made detailed measurements when they handle them. We know at the base they are 2-3 times as thick and 2-3 times as wide as the portion near the tip. We know that most Japanese swords even the Koto style livelier ones from the earlier period have a base at most 1.3-1.5 times as thick and 1.3-1.5 times as broad as the yokote line. It's a fact and physics, not some feelings conjured out of the back of our mind.

The mass distribution on a 36" original nodachi from the 14th century will simply make it never handle as nimble and precise as a medieval sword like this. Doesn't mean Nihonto can't be nimble. I already stated the shortening of the average blade over time is to ensure that. When you have a 28" blade it's certainly a lot usable. What's the nagasa of that antique tachi you own, the weight, the motokasane versus the sakikasane, the motohaba versus sakihaba? What's the edge geometry? Where are the pivot points and the action points? What is the tip weight? Where is the center of gravity? My guess is, it's not a nodachi and doesn't have a blade length hence reach and tip speed comparable to a longsword. It's OK, it stays short for a reason, for its characteristics that ensure the durability with the Japanese method and Japanese steel, but not ruin the handling. That is my point.

I didn't say Japanese swords are bad. Should that have been the case, none of us wouldn't give an eff about them. They are not better, they are not worse. It's OK, they were used by Japanese to fight other Japanese also with katana. They are different than swords from other cultures. Different challenges spurs different solutions. Ingenious solutions and ingenious craftsmanship and ingenious artistry. Just like swords from other cultures.

They are misconceptions, though. What you called "empiric evidence" (btw the correct term is "empirical evidence") are just some unsubstantiated claims with a link to some HTML pages or a PDF, which you happened to misquote. I can't see the relevance of your day job's existence. You are having this relaxed debate and "posting swords all day" without quitting it anyway (and aren't we all?) so what's the matter? 

I'm glad though that you called yourself out on misquoting Muneo Yaso's paper, is correcting a misquotation a "successful grad student learns" per your standard?
Hmm, now who would misquote a statement of "hardly harmful impurities" as "free of impurities or edge inclusions"? Again please understand carbon is impurity to steel, but it is also what makes steel, not pure iron that's not hardenable to make sword blade.

Even that paper itself isn't accurate or at least is inambiguous on this statement, but they sure wouldn't claim "Tamahagane is free of impurities or edge inclusions" because it would make them sound that they are claiming Tamahagane isn't even steel. Like I already stated in my previous post, impurities are not harmful. The specific content, percentage, or uneven distribution might be. In fact, different inclusions more often than not are there to introduce properties to different steels--hence the modern concept of tool steel and super steel.

As a matter of fact, it's wrong for Muneo Yaso's paper to make a blanket claim that elements like Mn and Si are "harmful impurities" that "decrease the sword quality". Let me share a source even though it's admittedly what "successful grad student learns": The Properties and Effects of Manganese as an Alloying Element. "In steels, manganese enhances strength, stiffness, hardness, toughness, hardenability, wear resistance as well as forging and rolling qualities." A small amount of silicon also improves the strength, ductility and hardenability of the steel.

It must be understood that these beneficial properties that the inclusions introduce to the steel can only be utilized by following very specific heat treat processes. So although the statement calling the inclusions like Mn and Si downright harmful in M.Yaso's paper is misleading, if we put it into the context of pre-modern Japanese swordsmithing, it might not be completely wrong, given Japanese swordsmith's obvious unfamiliarity with dealing with different alloying elements in heat treatment. Like I said, you could have the best steel, and heat treating it wrong would absolutely ruin it.

The inclusion of those elements won't "decrease the sword quality" as the paper suggests, but if the swordmaker has no clue of how to distribute them evenly and heat treat the steel properly, he would ruin the sword for sure.

I didn't claim Nanban meant the southern barbarian tribe that Liu Bei fought. It's a funny coincident it's the same word (南蛮) that Japanese described European people. Well, ancient Japanese people loved to use existing Chinese terms like nanbuchoku (南北朝) and Sengoku Jidai (戦国時代) just like the Romans liked to borrow terms from Greek. What I said in the previous post was "Nanban steel importation is a FAR later phenomenon, than the time when Japanese swordsmith needed to innovate to produce higher quality steel called tamahagane and use differentially hardening process (late-Heian period). So the supposed steel quality of "Nanban steel" is completely irrelevant. Even if we are to discuss the Nanban steel import, although "Nanban" means "southern barbarian" which denotes to Europeans, the steels imported by them were for the most part not European steels, but from neighboring cultures, and because of the mercantile nature, some of the import was of bad quality, others was of good quality. Kozan Sakakibara had commented that the Nanban imported steel was great for swords. It is of no consequence, one batch of import might share no common trait to another." 

I said specifically the "Nanban Steel" was primarily continental Asian steels (Indian, Chinese, Korean) brought to Japan by European trader not steel manufacturers, but may occasionally contain some European steels (given how much an overhead it was to bring steel directly from Europe on ships than buying steel in Asia and bringing to Japan to trade). In Japanese author, samurai, historian and arms & armor aficionado 榊原長俊's 18th century manuscript 本邦刀劍考 (Survey and Study of the Domestic Swords), he specifically stated the compositions and origins of the Nanban steel import (how the biggest portion of the Nanban import is of continental Asian steels despite being brought to Japan by Europeans), and how some of them are too brittle for plate armor, but great for swords. That is ACTUAL literature. I suggest giving it a read, rather than clutching at Markus Sesko one too many times like the Holy Bible, not to mention the uncertainty of whether you read his words right and didn't misquote him. After all, it's just one 21th century author writing in English. Reading a couple of paragraphs of his work, you are still largely lost in translation and several layers too far from first hand studies with empirical evidence that's provided by actual Edo-period samurais and arms & armor experts.



That is not evidence. That's a claim. It's not even a claim by anyone else. Like I said, because you cannot read Japanese, and don't understand that "tachi" in English is used for two different Japanese terms, 大刀, which is used to denote all single-edged swords prior to the 10th century, including Chinese and Korean ones, and Chinese and Korean-style ones made in Japan, and the ones used by the Emishi people not seen as Japanese. It's fundamentally different from the term 太刀, which is also translated as "tachi" in English, but it means a much later period swords that carry the signature traits of Japanese swords. Yes, a Yamato-school tachi of the 14th century would be a 太刀, not 大刀, even though in English you can't differentiate one "tachi" from the other "tachi". Seeing the word "tachi" used somewhere to describe an earlier sword isn't a proof that a 14th century style tachi existed in that early period. I get it, it's hard for someone who can't read Japanese, but try dispel your misunderstanding, at least.

There's absolutely no evidence to suggest the gyobutsu Kogarasu-maru sword presented to the Emperor is an original from the 8th century, none. It's not that I like it, or I don't like it. There's no evidence at all. The sword is a 19th century purchase by 宗重正. It has a kogarasu zukuri geometry, and this type of type geometry has been featured on many swords throughout different periods. There is no mei on the tang to link it to any maker. No carbon dating has been done to suggest even a time frame of its origin. Different swords with a kogarasu zukuri was mentioned in different periods of the history, sometimes in records, sometimes in mythology, but there is absolutely no indication that this particular sword currently in the Imperial Collection is any one of those mentioned in history, let alone the one told in the mythology of 天國安綱. Just because in legends and stories (many were made up in far later periods), 天國安綱 was said to have made a sword they called "Kogarasu-maru", doesn't mean this sword they also called "Kogarasu-maru" is that one, if the original one even ever existed.

A more sane speculation would be that should 天國安綱 really existed as a person, and very likely he did, as a mastersmith, he had made swords (not just one sword, that's not what swordsmithing works) of kogarasu zukuri, and you can call it "Kogarasu-maru". We don't know whether he made complete straight ones, like the Chinese-made tara-tachi housed at Shoso-in (note it's a single-edged blade with a long false edge and a tip geometry similar to double-edged swords, just like the kogarasu zukuri blade geometry minus the slight curve). He could have made swords with curvature, as we know the transition to the curved blade is a long process, and the change of the curvature with the fashion and technology kept going and went well into the 16th century. Blades from mid but mostly late Heian period started to sometimes feature a slight curvature, but some of the first to feature this are the Emishi people's "hair-tweezer style swords" and most of the curve was in the tang, not the blade.

If it's stated as "it's said that it was made by a smith in the myth", then they didn't expect you to take it at face value literally. Just like when they say legends say "Kusanagi no Tsurugi" in that box of Imperial Regalia is LITERALLY the sword found inside the belly of a eight-headed serpent slain by the God of Thunder.

I never said "tsurugi" means "Chinese swords" in Japanese. What I said exactly in that post was: "note the usage of the word "tsurugi" which denotes "double-edged straight swords" exclusively".
Also, "Tsurugi" doesn't mean "not Chinese swords", and it doesn't mean Buddhist talisman. It simply means any double-edge straight sword of any origin. And it's not a "talisman", it's a weapon that you can find on some Buddhist statues of Demon Slayers and Guardians, it's part of the statue, not a real tsurugi. You can also make the shape of a double-edged sword into a talisman, but it doesn't mean any talisman is a sword, or that the meaning of the  word "tsurugi" suddenly was changed into "talisman". That's not how languages work. Tsurugi is written as 劍 in Japanese Kanji, Jian is written has 劍 in Chinese. This is why Tsurugi is also called "ken" (Japanese pronunciation of the word Jian) in Japanese, because Tsurugi and Jian have the same meaning, they don't carry any connotation of the origin of the sword, just the geometry of the sword. 
Did I suggest they were dumb? Did I suggest you have to have a periodic table to forge and heat treat blades with steel? People anywhere else was heat treating these steels just fine and make lightweight and lively swords. So it's evident that one didn't need the periodic table to work on the steel, except for experimentation, and some attitude that doesn't brand anything they don't understand as "bad for swords".

I said it before, I'll say it again: the Japanese were doing more than fine making Japanese swords used by Japanese to fight other Japanese also wielding Japanese swords.

Why do I have to be familiar with Markus? Is this a bible study group of Markus' books published in 2012 or something? Why do I need to read books written by a modern person living in North Carolina to get lost in translation in hopes of some digested information, when I can perfectly read Edo period manuscripts written by ACTUAL Japanese, and ACTUAL samurai, and ACTUAL historical persons who wore the armor and fought with Nihonto?? The original texts are far more authentic, and reading the original language is the most precise way you can understand the subject.

The other thing is you keep bringing up Toledo, as if it's an all-encompassing term for medieval European swords. While Toledo steel had fame, and produced some swords of note, the swordmaking centers in medieval Europe were Passau, Solingen, and northern Italian regions as well, as the overwhelming majority of the surviving examples are from these regions. There are also tons of diverse sword groups beside even those centers, the Sempach family, the Castillon-Dordogne sword family, etc. It seems that you are not familiar with any medieval European swords, or perhaps swords from other regions, while we talk about comparisons, these knowledge would be helpful. Let's not laser-focused on Markus. How about some Edo-period Japanese authors on Nihonto? How about 小関永富 and 尾関善兵衛?

Besides that, there are just physical properties that are immutable. Things like dimensions and mass distribution, you can't just tank it. Like I said time and again, it made sense for Japanese swords to be on average short in order to still feel lively. There's a spectrum, of course, but the way they make swords emphasizing durability given Japanese's native steel source (the final result isn't necessarily bad, just a lot of more inaccessible to acquire than that of other cultures), dictates that they sacrifice handling and performance for durability, and they look in other places (rigidity of the blade, edge hardness) to compensate for that loss. That's human ingenuity.

Going back to the topic of Niku, there isn't actual disagreement here. Niku doesn't mean better or worse, it's one solution that has clear trade-offs. Antique Japanese more often than not have them, mostly for durability. Some would prefer having less or none. It's just like modern time, but only that modern practitioners concern even less about durability, and more about performance and handling, for obvious reason, but it's not like niku and durability isn't appreciated at large. So, yeah it depends, on the maker, and on the specific user.

Drunk Merchant. I never said Japanese sword steel was crap steel. Nor did I say Japanese swords designs or forging process was bad. I said there are specific reasons they evolved in the way they did. You need to look at their traits like distal taper in context. I never said tamahagane is bad sword steel, I said it was an inefficient way to to acquire sword steel, just like medieval Japanese people acknowledged. The most common iron sources (not all sources, they have rare good iron sources and sometimes good import steel sources) made it particularly difficult to produce sword blade steel. The traits like the commonality of niku and less distal taper, and on average much shorter blades are all to respond to durability given the steel source and difficulty to produce GOOD steel, not bad steel.

I said ON AVERAGE, and when sizes are comparable Japanese swords are less lively, I didn't say any given Japanese sword is less lively than any given European sword or Chinese sword or Indian sword. I only compared the average. I don't need to hold every single antique original example ever existed in history to make that observation.

Any given one example must be studied and judged on its own merit, obviously you can't predict whether it's superior in any aspect to any other arbitrary example. The spada de lato is a Renaissance sword, not medieval sword, and it's a single-handed sword, plus I bet the blade is longer so it's hard to compare apple to orange, not that I doubt your testimony that this particular example doesn't handle as well as that particular example of Nihonto.

On the niku we just have to agree, and on any other number of issues, unless you wanna pick out of some points and argument out of context to make it sound that either I said something ridiculous or we don't agree on.

On the original dating on the Kogarasu-maru, we just have agree to disagree. My take is that it's indeed a Koto passed down, but not the one created by a mythical figure, even though I don't disagree that a museum can link it to such a figure. I just don't want to take it at face value like the Kusanagi sword's claimed origin (even though I think it's cool), in the same way that I know for a fact that the sword they call Joyeuse at Louvre isn't one sword wielded by Charlemagne, because we know the style of blade let alone the fittings are not from the 8th century. I think it's cool that the museum brings up the legend about Charlemagne and his sword, but you simply can't objectively believe it's Charlemagne's sword.

On the author's matter, I never dismissed Markus' credit. I think it's just pointless that you keep mention that I didn't read Markus as a move. I may as well go read Markus' work, and you may as well get down to reading some antique manuscripts. That's it.