Kamitsure ~7 no Nijou Fushigi~

Mutsuki is a girl, but a 'boy' has always dwelled within her, helping and sometimes troubling her. This led to her parents' divorce and separation from her beloved twin sister Nanami. Years later, Nanami transfers into Mutsuki's all-girls school. However, her once loving demeanor has turned cold, leaving Mutsuki bewildered. Seeking answers, Mutsuki visits the school's legendary mirror in the concert hall, one of the seven mysteries. There, she is whisked into an 'alternate time' and meets a voice that grants her wish. Awakening in her room with a small mirror, the bonds between her, Nanami, and other girls begin to shift dramatically.