Ichi the Killer a question for fans

[dangermouth]

Have trawled the internet for info on this and just cant find anything. Ichi's still my fave movie of all time, but am still scratching my head over what probably is a very important part of it... Question is Is Kakihara human, or is there a subtle supernatural twist? There's little clues throughout that would suggest he has the ability to self generate.. if so it would also make more sense of the ending...

thanks in advance