Mai Kawai is a 20-year-old rookie police officer who joined the Okajima Prefectural Police seeking stable income, influenced by her father's desire for job security after his own unstable career. She lives with her parents and younger brother. Early dissatisfaction with police work, driven by mundane tasks and public mistreatment, nearly led her to resign until she met Seiko Fuji. Fuji transferred to her station, becoming her supervisor and mentor.

Kawai possesses a blunt, straightforward personality, often speaking without considering social cues or the mood. She appears careless in daily matters, like forgetting to lock doors, and initially lacks professional experience and physical prowess, struggling with martial arts and finding riot gear heavy. Despite this, she maintains a cheerful and positive attitude. Her exceptional observational skills, particularly in facial recognition, allow her to create accurate suspect sketches from vague witness descriptions. These drawings, stylistically odd yet effective at capturing distinctive features, aid criminal investigations and earn her departmental recognition. She is also registered with the Prefectural Police Special Female Unit.

Over time, Kawai experiences significant professional growth. She transitions from frequent complaints to developing pride in her role, actively striving to become an officer Fuji would respect. Her physical endurance improves, enabling her to handle previously challenging equipment. Mentally, she evolves from reluctance to embracing police duties, often considering Fuji's approach during critical moments. Her investigative skills expand beyond sketching to include meticulous evidence searches, demonstrating empathy for suspects' circumstances.

Kawai has no prior romantic experience, leading colleagues to perceive her as non-romantic material. However, reading romance comics sparks daydreams about love, and she becomes notably attracted to handsome individuals. She develops a crush on colleague Seiji Minamoto after he cuts his hair, though she initially feels uneasy around him. Her most significant relationship is with Seiko Fuji, evolving from idolization to a deep mutual bond. After a dangerous hostage incident in Saltani, they solidify their connection by exchanging matching rings. Kawai also admires Fuji as a mentor and role model, viewing her as a mix of a stern teacher and an older sister figure.

Her future trajectory includes becoming the first female head of the Okajima Prefectural Police Academy, where she plans to incorporate past cases into training materials, reflecting her journey from an inexperienced recruit to a respected police force leader.