First stunt is for "dual wielding" then a second stunt for the mouth weapon...
Basically when wielding three weapons you get a +2 effect on attacks that inflict physical stress (basically you up your Weapon:X rating by 2).
But you would of course need an aspect relating to your unorthodox fighting style (Biting the Third Blade?). Maybe an aspect also related to your initial master. Those could be your Phase 1 and 2 (or Phase 2 and High Concept).
I hesitate to say it is very much a gimmick, but I think everything about One Piece is supposed to be a gimmick.
So just be audacious with your aspects and stunt names (I mean, I know everything should be audacious).
"Three Blades, One Swordmaster" (hopefully this suggestion won't create millions of reaction videos of people vomiting). I have no idea for what it could do (maybe it is your version of "Wall of Death")