NocturnaL

It is an anime adaptation of the manga by Monorino.

Etou is a student who, for a long time, has been in love with his classmate Sayako. One day, Etou witnesses the attack on Sayako and immediately helps him. However, when he thinks he has saved the girl he loves, Etou discovers that the latter is completely different from habit. Indeed, Sayako has two personalities. During the day, she is a kind and modest person, but at night, she turns into an insolent and lustful person.