Ai Mizushima is a woman in her twenties with brown hair and brown eyes, conventionally attractive. Her past is marked by tragedy when her parents were killed as unintended bystanders in a gang shooting. As the sole survivor, she was taken in by the gangster boss Komatsu. Discovering the Hazakura gang was responsible, she dedicated herself to avenging her family by targeting their leader. She works professionally as a hitman under the alias "Speeding Bullet of Komatsu."

She strategically interacts with the male protagonist, Jin. Aware of Jin's friendship with Suzuki, who has ties to the Hazakura boss, she approaches him to extract information on the boss's location. To facilitate this, she proposes a wager: if Jin can sexually satisfy her to the point of eliciting a vocal reaction, she will reward him with a Shelby Cobra sports car. This challenge serves her dual goals of locating the Hazakura leader while providing personal diversion and relaxation before her planned confrontation. Her demeanor blends calculated intent with a degree of personal interest in Jin, though her primary focus remains achieving vengeance.