Based on a shounen manga by Yuuki Masami, serialised in Shounen Sunday.
Tsutomu Senkawa is an average high school kid who is busy studying for his senior entrance exams. Tsutomu goes out for some fresh air, after a hard day's work studying for a big test, when he runs into a guy fleeing from a pretty young lady. The pursued man is actually an interplanetary criminal on the run from a Federation agent called Birdy Cephon Altera. Caught in the midst of this chase, Tsutomu gets thrown by the man at Birdy, which kills Tsutomu. Fortunately for Tsutomu, there is a way to keep him alive, although it comes at the price of discarding his body. He ends up merged into Birdy's body.
This is a remake of an older manga/ movie. 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. Birdy and Tsutomu are forced to keep their shared body secret while still investigating a group of aliens experimenting on humans.
TETSUWAN BIRDY (鉄腕バーディー) is the title of Yuki Masami in several series (OVA, manga and TV). The original manga from 1985 to 1987 published in the magazine Weekly Shonen Sunday and later abandoned with only one issue. In 2003 began a new version of the series, with a totally different style and was published in Weekly Young Sunday 2003 to 2008. Upon completion of the journal title was in the magazine Big Comic Spirits which is currently published. The 22 issues were published from 2003 to 2009.
An anime adaptation called TETSUWAN BIRDY: DECODE (鉄腕バーディー DECODE) aired from 2008 to 2009.