High school girl Kanzaki Mitsuki "inherits" an older brother when her mother remarries a fellow divorcée with a son. Soon after, her new stepdad is transferred overseas and her mother follows him there, leaving Mitsuki to live alone with her new stepbrother, Yuya. Feeling abandoned by her mother, she stays distant from Yuya, never really getting along very well with him nor even keeping a conversation with him. One day, Mitsuki is visited by an angel/ghost named Hiyori, who takes over her body and makes sexual advances towards Yuya. Hiyori is the lost spirit of a girl who in life loved Yuya deeply, however she died before she could confess her feelings and thus can not reach the gates of heaven and obtain eternal peace.