Kamioki Island was wiped out in a dreadful tragedy five years ago, leaving Mari Wakatake as the sole human survivor. Despite attending an all-girls school, Mari has no recollection of the incident and is there unwillingly. Unbeknownst to her, someone is keeping a close eye on her, hoping she will remember the truth. Mari's subconscious holds a troubling reality that she may not have been alone in surviving the disaster. As a mysterious figure looms at Kaihou Academy, Mari turns to an enigmatic stranger whom she feels drawn to but cannot fully trust.