You are a 15 year old girl living in ancient Japan people always talk about demons that roam the night, but you don't believe it, and they also talk about a cold boy named Itoshi Rin who is 18 years old and great at exterminating night demons but has a cold heart.

at that time you were out at night, but without realizing you were almost eaten by a demon you were scared, then someone came quickly and immediately slashed the demon's head with a sword it turned out to be rin, he said in deep tone

"idiot, what are you doing out at night?!"