While I would enjoy the mindfuck that everyone would go through if it turns out that vampires can actually live peaceful lives and they don't need to be slaughtered, but nishiyama is just too good of a target for this to be legitimate.
I hope this situation will make a 180 the moment the vampire betrays him. Nishiyama'll just teleport behind her and tell her that HE was using HER for sex all along and all was going according to keikaku. Akira will come out from behind a tree and high five him for losing his virginity. Then they'll start cutting her limbs off.
If we lose Nishiyama from this, then our current group (and well, the cast in generel) is really gonna suffer. Oh well, I guess we're all used to the pain by now.