Jenshin I think you've got the point, and that maybe explains why killy changes his expressions along the manga, like, he let the little boy died and the other guy who thinks killy's a doctor on vol.1, on vol.2 he kills some guys of the same specie of the one he saved before i mean, he got betrayed by that only-head-guy. then he mets cibo, she get in sanakan bodie, he met another cibo, the 1st cibo disappears with the death of sanakan that killy is obligated to kill for his safe and the 2nd cibo appears again. then, that cibo dies or something and appears a 3rd cibo who I don't know if it is the 1st or the 2nd and also appear lots of enemy-cibos, I mean, isn't that too much for just one guy to take?
It not just a fisical battle that he's fighting there :?
In the last volume he doesn't care about anything anymore, except to find the NTG
(someone please correct me if i'm wrong)