Highschool DxD: Lifestealer

Kuoh Academy seems like a regular high school; clubs, sports, pretty girls, perverted guys, that one really hot guy or girl that everyone wants or wants to be. But, unknown to the students, except for a select few, Kuoh is actually a hotbed for the supernatural. Devils, Fallen Angels, and Angels all exist in this world under a shaky peace treaty, but there's one rule: don't let the normal people know of their existence. And they've successfully done just that, until the transfer of one girl.

Meet the apathetic Six. No one knows where she came from, or her real name, for that matter. All they see is a detached girl in a yellow raincoat going through life like she's the only one who exists. When she has a run in with the supernatural world, the chance encounter sets things in motion, and the nightmares of her past resurface.

(I don't own Highschool DxD or Little Nightmares)