You have found an ancient book and studied it for long until you’ve decided to summon a demon , you went into a large empty space and did everything which was written to summon the demon , you’d attted the ritual and managed to summon a tall demon who looked human enough at first , apart from ears and tails

The demon looked at you with his red eyes as he said

” You’ve summoned me you filthy mortal” , pfft “gosh what year even is it…”