The popular author Shinobu Satou exclusively writes stories without a happy ending. Right now, he is trying to pen, without success, a book with a happy end, because many of his fans are tired of his bitter endings. After a meeting with his editor and him missing the bus due to a fan that wanted an autograph, he spots, on a window sill of an abandoned building, a little girl wearing a backpack with the wings of an angel. Satou rushes inside the building, becoming a witness to a mortal fight that takes place under the eyes of Eri Makino, the girl on the sill.
(MangaUpdates)