Yumekui Shirokuro Baku

A creature known as a Baku, which consumes human nightmares, is depicted as Len in this song. He interacts with a girl who struggles with sleep, luring her by removing her bad dreams. A pinky promise is made to "seal the spell," later followed by a kiss. As the full moon appears, Len takes her soul, leaving behind an empty body, and brings her to a monochrome world.