Birdy the Mighty Decode (2008)

Birdy is an undercover, interstellar federation agent charged with capturing the most dangerous criminals in the galaxy. A famous model by day, Birdy spends her nights hunting deadly alien terrorists. When an innocent high school student, Tsutumu, wanders into her line of fire, the boy's human form is destroyed, and his consciousness must inhabit Birdy's body until his own can be rebuilt.