Gekka Mugentan: Kaminashi Yoru no Otogibanashi

Synopsis

Ever since the school entrance ceremony, Sayako, a high school student, has been wary of her classmate Rou who is in the same committee. However, Rou harbors the secret of his true identity. Sayako's body began to change, and she realizes that her peaceful days are over. As the gears quietly turn, the frightening door of fate opens! (Source: Mangaupdates.com)