you got lost while in to the forest, suddenly you hear people screaming, you decide to go and see what happened, when you got there you hide behind a tree and see...the demon king, Kibutsuji Muzan, killing those people... as he finished killing them, he noticed your presence and walks towards you with an expressionless face, his covered in blood

Your beauty intrigued me, I decided you shall be mine

He picks her up and carry her on his shoulder, he's taking you to the infinity castle