Birdy the Mighty: Decode

Tsutomu, a perfectly average student, is busy studying for his high school exams when he stumbles into a police chase in progress. Caught in the crossfire, the boy is hit and on the verge of death when he's approached by a young woman. Birdy is on the scene and, by joining her consciousness with his, manages to save him from his imminent demise. Now they share a body and will have to learn to live together as she continues her career, capturing criminals and saving lives as an interplanetary police agent.