we kill humans all the time in videogames, i doubt that'd be a problem. i just don't know how sensitive he would be to combat overall. how gory is too gory? castlevania at least has a parallel in that the dracula's castle is kinda like the hotel, being able to appear anywhere and reshape the internal layout, along with having been around across many generations.
oh wow, the valley even spawns monsters to specifically torture asterion. conceptually this could go really wrong, in hitting too close to home, or really great, as in him taking it as having a chance to fight back his traumas in a safe space.