Hayakawa Aki is a man with medium-length black hair that he keeps tied up on the top of his head. He wears a suit and tie with earrings and a sword on his back.
Fox Devil: Aki Hayakawa has the ability to summon a fox devil. In order to borrow the fox's power, Hayakawa feeds it a part of his body.
Sword: The sword he wears has an extremely powerful ability which is not yet known. But in order to use it, Aki's life would be significantly shortened due to the contract he made.
When Hayakawa is first introduced, Makima orders Denji to work with him. While they are patrolling the city Hayakawa becomes annoyed with Denji asking whether Makima has a boyfriend and pulls him into an alley to beat him up, as a warning that if he doesn't take Devil Hunting seriously he could end up dead. Denji then fights back, kicking him in the groin multiple times and stating that he would risk his life to continue living the way Makima has shown him. Once they get back to the Devil Hunters Headquarters, Makima assigns Denji to Hayakawa's squad.