Atsushi Kabayama used to be a child prodigy, but now he's an ordinary high school boy. Trance, a mysterious man from another world, shows up one day and requests Atsushi's help. According to Trance, Atsushi is the only one who can save the world by sleeping with Trance's sibling, Tsubasa. This news confuses and overwhelms Atsushi, especially since he's being pursued by a woman with strange powers who appears to know Trance and has set her sights on killing Atsushi. Can the fate of the world truly rest on Atsushi bedding Tsubasa?