As a sometime practitioner of both European AND Japanese fencing styles, allow me to point out a few differences between them, and implications for the proposed combat system, particularly in how to handle speed and binding.
Japanese weapons are often considered superior to European. This is not technically true. It is true that against an un-armored opponent, the katana will win almost every time. Even against a lightly armored opponent. A katana is sharp, and can cut. A katana is also lighter and faster. But the Europeans never made katanas, and for a very good reason. That sharpness is WORTHLESS against heavy armor, which the Europeans had -and the Japanese lacked-.
European Weapons
A European heavy armor battle is made not to cut an opponent apart, but to bash his armor in and sever things like a woodcutting axe. There needs to be some good mass there, and the "edge" needs to be able to withstand a beating, so it's kept mostly dull. The wedge is there to optimize the crushing of armor, and you'll see this even in their maces which were flanged. Those edges, insufficient to cut, can really make a good dent in metal, and it's enough of a wedge with enough power that it can RIP flesh, if not slice it.
The downside is speed. Longswords need some hefty windup and a lot of power to get enough energy to go through armor. Lesser strikes work too, but even these have to be enough so that while the hit won't dent (and kill) the opponent, they'll knock him off balance or shake him about (like softening up a boxer, working towards delivering a concussion). This takes a lot of energy, and means that theres a considerable amount of windup to perform. This is true even against the unarmored, because you need to tear, not slice.
Now remember, the Japanese LACKED heavy armor. The best armor they had was banded or ring mail, not heavy plate. Many had only leather, or were completely unarmored. In this situation, an edge will, quite frankly, grant you an edge.
Japanese Weapons
This edge has MAJOR and MASSIVE implications on combat. Let's go back to europe a moment. To use the numpad system, Europe would find use for all 8 digits, because the windup is needed. Starting out at 6 or 7 or whichever opens up half your body to attack, but it doesn't matter too much, because your opponent needs to wind up too, and by the time he can take advantage of the opening, your attack can be modified into a defence, or if he doesn't take advantage, your attack can remain an attack. If he attacked your opening without winding up, it'd hardly matter, because the attack would barely hurt you without the power behind it.*
Japan doesn't have this problem. With an edge against unarmored or lightly armored flesh, the slightest touch is basically a kill. As far as Japan is concerned, a katana is a lightsaber. (As far as Europe is concerned, a Katana is a toothpick-- if heavy armor is available) If two swordsmen are in range of each other, and either one moves to either side (7, 4, 1 / 9, 6, 3) then the other can rapidly rush in with an 8-5 strike and kill. The person who started won't have the chance to finish.
This means that while European fighters can always use the whole numpad, Japanese fighters who are within range of each other use NOTHING but 8-5. They won't even touch 2, because their weapons are single-edged and being so low is thus ineffective. (Kendo Kata #1 teaches that anyone who goes too low in a strike is dead). Only when outside of each other's range will they place their swords in a 1 or 3 position, and this is mostly to trick the opponent into misjudging their range (does he have a 40 inch blade or a 60 inch blade? When will he strike? The rear 7 position hides the lenge of the blade very well)
Enter: Wristwork
Yet, with only the 8 and 5 positions available to them, they can strike a HUGE range of targets via two means. The first is footwork, stepping to the side before making a strike (Kata #2 teaches that a sidestep can both be a defensive move-- getting out of the way-- and an offensive one-- opening up an undefended area in the opponent while keeping yourself safe). The second is in twisting the sword.
Consider that 8-5 is the most optional move you can make. Consider that two Samurai approach each other. Both Samurai want to cut 8-5. Both Samurai know that the other wants to do exactly the same thing. So there is no surprise comming, because anything surprising would be death to the one giving the surprise.
So Samurai A comes in to cut 8-5. Samurai B reacts, but when he comes up to 8, he twists the blade slightly. This twist, adding maybe an inch, maybe even just half an inch to the area his sword covers, will knock the A's blade completely to the side when they bind together near A's hilt. Now A's blade is located at 7, and as I established before, being at 7 is death. Samurai B then twists back to normal, completes the 8-5, and kills.
The stomach, in a horizontal strike, can also be hit with a combination of 8-5, footwork, and wristwork. What happens is that if you're fast enough, you can run past the opponent while he's still at position 8, come down to 5 to his side, twist the blade, and then as you pass cut his guts open.
Now, European longsword uses similar wrist twists, which is why I really think it's crucial to the combat system, but Katana RELIES on it. Every move is 8-5, so you may as well not even bother with the selection interface for it. But every 8-5 move is VASTLY different with wristwork. Footwork and wristwork are the ONLY things differentiating moves. Longsword has the full numpad AND footwork AND wristwork, and being better at each means improvements.
*Footnote: I don't want you to think European fencing is a VERY slow, cumbersom thing. When I say slow, I mean relatively so, where the relation is the ratio of your speed to your opponent's speed. The actual fighting will be VERY fast, especially to an observer.