Birdy the Mighty II

Note: This series is different from the other "Birdy the Mighty," even though it's from the same mangaka.
This is the remake version of Tetsuwan Birdy. While pursuing a criminal, the pretty but reckless interplanetary police officer Birdy Cephon Altirra accidentally kills Tsutomu, an eartling high school student. To make amends, Birdy is forced to share her own body with Tsutomu's spirit so that he can continue his own life. At first, Tsutomu knows nothing about his situation but soon discovers that his body is starting to take certain actions without his mind ordering it. In times of action, Birdy takes full control of their shared body, transforming it back into her original female form
"The original manga ran in what is now Monthly Sunday, but when Masami Yuki began serializing Kyūkyoku Chōjin 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