Everyone's getting upset, but I honestly prefer this to the power of friendship asspull ending I thought we were just about to get- at least here someone is ACTUALLY doing something smart to stop the demon instead of just telling him to stop. He is INFECTED, directly, by the progenitor of all demons as part of his dying wish and a simple "believe it" ending would be so damn lame.
Of course we could still go friendship power ending, there's more to come...