First entry in the 4th Unit franchise.

Yuusuke, a common boy back from school, finds a naked girl in the forest while searching for his hidden bike. She is amnesic and only remember a name: Blon-Win.

Four days ago, a mysterious battle between unidentified aircraft occurred above Tokyo. One of them, shot down, felt in the same forest the girl was found. The authorities never found any body in the debris.

Might this girl be linked to this case? This is what she is decided to discover.