All Hail Lelouch said:
Who would it be?
Personally, I would LOVE to steal Domon Kasshu's SHINING FINGER! Just so I could say that awesome speech every time i use it.
What about you?
DAMMIT! NINJA'D BY THE OP!
My second choice would be...
Being Batman. That's Batman's signature move. BEING Batman.
In all seriousness: The Mangekyo Sharingan eye. I'm not a big Naruto fan, but even I admit that eye is f***ing SWEET! apart from the whole "going blind" aspect...
edit: NINJA'D AGAIN!
ok... let's try this again...
"Haki" from One Piece. Seems pretty awesome from the little that it's been seen.