Instead of seducing him, she should have just tied him and explain the situation untill he assumes his new situation.
But no, we keep with the traditional vampire lore of lusty entities.
I definitely should have expected goofiness from a manga where the MC is saved by a loli vampire bursting from the ceiling, and yet here I am, dumbfounded.
I highly doubt about werewolf theory, lol. But, his last name, Mikogami , maybe indicates on connection to some magic stuff. "Miko" - priest + "gami" - god. Shrine bloodline?
I think she turned him cause she can't defeat the antagonist alone, like from a strategic point of view it's better to gang up on someone then try to 1v1.