The seven genius students, known as the Great 7, launched a project to construct an artificial island called Nanae Island to realize their leader Ryuugajou Nanana's vision.

Twelve years later, with a total population of 100,000, and with as much as 80% of those inhabitants being students, Nanae Island has prospered as a special student zone. One of the island's latest residents is Yama Juugo, a high school student who has just transferred to the island, after being disowned by his father. One day, Juugo finds in his apartment the earth-bound spirit of the late Ryuugajou Nanana, who was murdered 10 years ago! Juugo's plan of living alone is suddenly thwarted by this strange room-mate...