A remake of Birdy the Mighty.

Birdy Cephon Altera is a Federation agent chasing interplanetary criminals to the planet Earth. While in pursuit of one such criminal, she accidentally kills a high school boy named Tsutomu Senkawa. Fortunately for Tsutomu, there is a way to keep him alive. He ends up being merged into Birdy's body and must remain so until the repair of his body is complete.

So, Tsutomu is stuck sharing a body with an attractive, strong, and impulsive space police agent while trying to keep his family and friends from finding out about Birdy. In the meantime, Birdy continues her investigation. Together, they take on a secretive group of evil aliens planning to perform experiments on the unsuspecting inhabitants of Earth.

"The original manga ran in what is now Monthly Sunday, but when Masami Yuki began serializing Kyuukyoku Choujin R in the pages of Shonen Sunday it began appearing infrequently, and was eventually abandoned. Only one volume was ever collected. In 2003 Masami Yuki moved from Shonen Sunday to Weekly Young Sunday, a seinen magazine, and began drawing a remake version, starting the story from the beginning." --Wikipedia