i'd be a vizard or something probably...
probably evil....as im just that sort of guy
but my Zanpakto would be enfused with darkness leading to a black blade which is constantly shrouded in black fog...and when it slices someone, the black fog acts as a poison and enters the enemy's body,i then could use this to destroy my enemy internally...and in bankai, it'd become an extremely long Katana with a red tint on the black edge, which would manipulate spirit particles allowing me to fill the area with my Dangerous and all-engulfing fog....and focus the fog into attacks.....
....i have TONS more ideas for Zanpakto's....