Tsutomu Senkawa is an ordinary high‑school senior who devotes most of his time to studying for the upcoming entrance exams. After a long day of studying, he steps outside for a breath of fresh air and encounters a man being chased by a young woman. The pursued man turns out to be an interplanetary criminal fleeing from Federation agent Birdy Cephon Altera. In the midst of the chase, Tsutomu is caught up in the conflict; the criminal throws him at Birdy, an act that results in Tsutomu’s death. Nevertheless, there is a method to preserve his life, though it comes at the cost of discarding his body. Ultimately, Tsutomu’s consciousness is merged into Birdy’s body.