Any tip to beat longsword using the katana?

(drink)

Excellent points. I entirely agree. The katana is very specialized. I imagine wrenching a katana from someone's hands would actually be more risky than doing the same with a longsword, as a katana is typically sharpened more and doesn't have as many leverage points. A cross guard can provide leverage for an enemy to wrench it out of your hands. A tsuba? Not so much

The massive two handed swords were Great Swords, not long swords, and were used mainly on the battlefield as a kind of polearm.  The bastard, hand and a half, and slightly longer handled variety were all longswords, which were only a few ounces heavier (and 25% longer) than katana, but had a closer POB.  It is blade on blade (binding) that gives the longsword (along with the many other reasons...reach, guard, double edge) inherent versatile superiority to the katana.  Again, user ability still trumps all, as a skilled katana wielder would turn a bum like me (holding a longsword) into a pile of dead meat.  It is better to use something that you really like (and so, would become good at), than something which may offer more general versatility, but your not interested in, so don't practice at and become skillful.

I dunno if I'll say a long sword is superior. It's all applications. When it comes to sparring in HEMA? Naturally the long sword shines. It's what it's made for.

The sword-taking I have been taught and done is 99% concerned with controlling the handle (after, of course you've gotten out of the way!).  Touching the blade is not really necessary, there's some where you do use the back of the blade, but it's more of a follow through after breaking his control.  Application-wise, taking the sword is nice and all but the over all goal isn't to take his sword out of his hands, it is to win.  If he's obsessed with keeping a grip on his sword and not letting you take it, then he's not protecting his face so BAM.  It's kind of the same thing with just about any other technique - if you're dealing with a clown who thinks that stopping you from doing your technique means that he wins, then it's practically a given that he's handing you all kinds of cool stuff.

The fun part of the 'wrestling' is a lot of people put themselves in really awful positions after delivering their attacks.  They get so caught up in CUT that they don't really understand how to recover (there's a little more to it than just snapping to a guard or kamae!) and may as well give you their center with a bow on it presented on a silver plate.  I put the single quote there because there's a difference between skilled wrestling / ringen / jiujutsu and white knuckled flailing / struggling so there wouldn't be confusion about looking down on wrestling or something.  Just thought it was worth sharing since it's a different mentality to what might come to mind when thinking about "wrenching" a sword out of someone's hands.

You are not talking about a massive distance - even if you assume three entire feet between the crossguard and the tip of the sword, you're only talking three feet. That's a distance anybody in moderate health can cover in the blink of an eye.

The difficult part isn't closing distance, the hard part is keeping your cool when someone is swinging at you so you can respond properly.  If you can sort out whether you walk forward to the right or forward to the left, that distance isn't nearly as big of a deal as you think.  Anything he throws your way HAS to be from the right to the left, from the left to the right, or down the middle.  If you don't freeze up and respond in time you've got a two out of three shot of being right.  Then you are in position to do something to him.

That's a controversial thing and can easily pull this way into a tangent though.

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With manipulating distance, you get yourself into a more advantageous position ready to work.  The other guy has to be at a disadvantage - if he was prepared for the close distance then he wouldn't be threatening at medium to long, he'd be waiting for you in half sword or have his dagger out or something appropriate for hugging range.  It's literally changing the rules mid-game on him, by the time he figures it out he should already be defeated.

It doesn't seem like it should work, but it does. I actually just *~-=CAREFULLY=-~* grabbed my ww2 gunto by the blade with just a standard grip like you'd hold a hammer and lifted it off the ground, it works. If you or anybody else does something like this at home I'm not responsible!

What you don't want is someone giving it a hard push or pull while you're holding it, unless you go along with it. Tight hand, loose arm means you've got some travel before it cuts into you. Tight arm loose hand means stitches ;-)

The feeling of the edge pressing onto skin is pretty unnerving - I'm sure with acclimation you can get used to it.

So with that, IF the other person's blade is not in motion, you can grab it. Whether it's because they are hanging out in a guard, they finished a cut, or you managed to get a hard stop due to something like a block, you've got a moment where you can grab.

If you've partially grabbed and they start pushing or pulling, get ready for fillet of hand and finger sandwiches.

I'm going to state again that I don't like this, to my knowledge there isn't anything quite like it in the system I study, and it feels reckless.  I can see where it could work and I know that people have filmed themselves clubbing away at a tire pell like it was a baby seal.  I just wanted to test it.  It is possible.  Whether it's something you want to do or think is a good idea is your business.

In specific application, the katana "can be" better, like (Ko Katana) under my bed (walls, ceiling, furniture, etc...).   On open ground, Longsword in all realms (Generally, of course). Whether sniping from distance (25% longer but barely heavier, and closer POB), or grappling (blade on blade/binding).  Katana was designed for a quick strike flesh cutting ceremonial duel (think gun slinger).  That longsword double edge DOUBLES your attack angles.  On paper, these physical attributes MUST be an advantage.  The Katana can cut better...but a completely decapitated man is just as dead as one where you chopped his neck beyond the spine.  There are some YouTube videos showing binding attacks where a simple twist (after blade contact) simply skewers the opponent (kind of like a short spear). 

Still, I would not like to tangle with one of those "great sword" wielders, as they were highly trained and competent with the weapon (they were indeed paid double wages, in fact).  You (probably a very powerful man) get that thing going in constant motion to cut pikes, spear, men and horses with that heavy blade.  One on one, on even and open ground, you still have to time your attack well in order to get to him before he sweeps you like a scythe cuts wheat. 

A polearm, with its extra 2-3ft. of reach advantage (another animal, really), ability to grab (manipulate) most of its length, and lighter weight, make it an infinitely better weapon individually or on the battlefield.  Remember, you can simply choke up, step back (or both) with polearms, so the "danger zone" remains constant.  The "myth" came from comparing longswords (which, more or less, WERE bastard, hand and a half) with great swords.  Great swords were much heavier than long swords (from a third heavier to twice the weight), as you could easily wield a long sword (2 3/4 to 3lbs.) with one hand.  Great swords were niche weapons, almost exclusively used on the battlefield against pike, spear, polearm, GROUP formations, not individually.  An equally experienced longsword wielder would be at a significant advantage, one on one, against a great sword wielder...and an equally experienced polearm wielder would simply destroy, as there is a reason polearm was king of the battlefield for thousands of years.  Still, nobody would want to run up on a great sword while it is in battlefield (constant figure eight) motion.