Wakatake Mari is the sole survivor of a tragedy in which all the inhabitants of Kamikakushi Island suddenly disappeared one night. Four years later she transfers to Kaihou Gakuen and meets Senkoji Hagino, the beautiful school council president school idol. It turns out that Hagino is an alien sent to Earth for reconnaissance prior to an invasion and was the one responsible for the incident at Kamikakushi Island. As Hagino interacts more with Mari, she begins to uncover more about human nature and begins to question the mission to invade Earth.