Tsutomu Senkawa

Tsutomu Senkawa is the deuteragonist of Birdy the Mighty. An average high schooler, Tsutomu ran into Birdy Cephon during one of her missions, she confused him for the criminal she was chasing and killed him as a result, his mind having been transplanted into Birdy's head in order to save his life, both of them have to learn to live with each other and respect each other's occupations while trying to keep their secret hidden from everyone in Tsutomu's life.

Personality and appearance
Tsutomu is teenaged young adult, he is often lazy and unproductive, in some incarnations, he takes interest in exploring old ruined buildings, a hobby which cost him his life. Before fusing with Birdy, Tsutomu had to wear prescription glasses due to his poor eyesight, however in the original manga and the OVA he did not need any glasses. He has short black hair and brown or gray eyes depending on the continuity additionally he wears plenty of different outfits throughout the series though is commonly shown with his student uniform, during one occasion in the reboot manga Tsutomu attempts to disguise himself by wearing his old glasses, a cap and a shirt that has the transgender symbol. When under the control of Birdy, his eyes change color to light blue, indicating she controls him.

Tsutomu's personality changes greatly throughout the story, he begins as a very anxious kid, terrified of even Birdy herself, and cautious of everything new in his life, depressed about his situation, it affects his ability to succeed in school, as the series progresses Tsutomu becomes braver and braver, he begins to cooperate with Birdy more and more as he realizes that helping her would also help him and his world, he helps Birdy by teaching her human etiquette and using his knowledge of general human history and helps her reveal several criminals. Although not as much as his buddy, Tsutomu too is somewhat quick to anger, he eventually develops a sense of justice just like her and attempts to act on his emotions more than once even when Birdy or others try to stop him from doing reckless things.

Despite fumbling at first, Tsutomu ends up being able to get used to his condition with Birdy and able to effortlessly change between her and his form, he gets used to talking to her out loud which makes a lot of his acquaintances believe he is going crazy. It is implied in the reboot manga that it's likely some of Birdy's traits have leaked into his consciousness and the other way around, it's explained that if allowed to continue their personalities would merge and both of them would cease to exist in order to create a new person, in Decode It is said that Tsutomu's mind will take over Birdy's instead.

Background
Not much is shown regarding Tsutomu's history before the story begins, however from the reboot manga, we know that he used to ask Hazumi help with home work and that they used to be closer together.

Natsumi Hayamiya is his best friend since at least grade school and knows him better than even himself, in the reboot manga it's mentioned that Hayamiya knew him so well that she knows about his scar on his butt and his problematic teeth situation, things which she later uses to investigate his real identity as Birdy's body is resistant to injuries and thus does not contain them.

He befriended Ryota Sudou and Kazuyoshi Chigira later in life.

Abilities
Being a normal human being, Tsutomu does not possess any real unique ability of his own, aside from fairly good deductive skills, all of his abilities are those that he gains from Birdy.

Strength: rarely, Birdy takes control of, or grants Tsutomu with her strength in order to perform tasks in scenarios where she mustn't be seen, she may also grant him:

Speed and agility: for the same reason as mentioned above, sometimes Birdy uses Tsutomu's body and her speed and agility at the same time in scenarios where she mustn't be detected.

Durability: thanks to Birdy's genetics, Tsutomu can stomach many hits before he is injured, however because he is a mere human he may still faint.

Transformation: During one scene in the 11th episode of Decode, thanks to his distressed emotional stress, Tsutomu was able to wrestle control of Birdy's body and briefly able to force it to transform to his form against her wishes.