Birdy Cephon Altera is a Federation agent in pursuit of intergalactic criminals. Her pursuit of two such criminals leads her to Earth. In an altercation with one of these criminals, Birdy accidental kills the Earth teenager Tsutomu Senkawa. Fortunately for Tsutomu, there is a way to keep him alive, by allowing his consciousness to share Birdy’s body until his own body is repaired.