[Yako]

I think it should work well enough.

You will want all the spells and special attacks as powers and give them a good amount of FP cost (I do suggest Rev. P Kitty's houserule for a bigger return on that limitation).
If you want, you can also add takes recharge to make it closer to the deck command style of games.

You could even emulate the deck command system with modular abilities if you want to amping up the recharge time and eliminating the FP costs.

If you use an MP system, you likely want to use Energy Reserve from GURPS Powers.

I think Heartless should at least have fragile (Unnatural). Maybe add Hard to subdue to make it less easy to just knock a heartless down due to low HP.
Alternatively, just let them fight to 0 HP and be killed then and give them more HP to make up for it.

Since heartless really have all sorts of attacks, it may be a bit tough but also interesting to stat it all out.

For heroes, super Jump and a couple of other traits to simulate the movement abilities will be necessary.

Use A LOT of acrobatic dodge to simulate the dodge roll mechanics.

Also, everyone will be summoning their signature weapon, which tends to return to them when needed, so they would be gadget based innate attacks with switchable (they can be summoned from nothing), but given that they can be neither destroyed or stolen by normal means (Riku taking over the Keyblade was a very special case), the only thing you would get out of it is the fact that keyblades can be knocked away to cause you a temporary inconvenience.
Keyblades also come with added abilities like extra energy reserve and gadget based magery or such on occasion, which should be packaged together with them.

You will make copious use of alternative attacks / abilities for multiple keyblades available as well as for the different spells, special abilities or commands.

Make use of Dirty tricks and similar to simulate the way Sora and company occasionally use situation commands and such.



As in many cases with GURPS 8but that will apply to other systems too), you WILL end up having to invest a lot of work to stat up all the enemies.
Heartless have so many creative abilities that, as said before, it may be hard to work everything out.