Here is the page for Onimaru move set brainstorming. I know @GRAG had a lot to say, and the moderators too.
As for me,
Far reaching normals like hakumen, so fairly midrange in terms of fs (we'll leave full screen to Arg and BBB [rip team staff ;_;)
B: maybe a bad uppercut
C: chargeable, level 1 is nothing but a slow big chop (or horizontal slice), 2 is armor, 3 is unblockable. Maybe he can slowly slide forward like kirby's hammer. Maybe this move is 2 damage to justify a special?
Air B: just throwing out an idea, but maybe a forward spin (like sonic but only once) with his sword and then he hits the ground. Maybe lots of block stun and pushes them back a bit, but lots of recovery frames
Super: an absurd OHKO? or at least stupid big damage? I think as a counter that's complete BS because it can be done on reaction
Air super: clockwork army, maybe like sentinel
Also talk of his normal grabs do 1, but his yomi counters do 3 (or at least 2)
I'll let Grag add his 2 cents, I can't remember everything