Teppei Yumoto, a 42-year-old detective in the Tokyo Metropolitan Police Department's Modern Crime Prevention Task Force – known for housing officers with disciplinary histories – sports an undercut hairstyle tied into a short ponytail and often appears with his eyes closed. His attire typically features a pale pink jacket over a dark purple dress shirt, linen-colored pants secured by a brown belt, white and brown loafers, and a silver watch on his left wrist.

He exhibits a personality marked by aggression towards higher police divisions and a passionate enthusiasm for gambling, particularly horse racing and boat racing. This preoccupation frequently distracts him from work duties, leading him to prioritize studying racing forms or placing bets over investigations. Despite this, he demonstrates dedication to his detective role and harbors fierce resentment over the dismissive treatment his task force receives.

Yumoto's underprivileged background starkly contrasts with the extreme wealth of his colleague Daisuke Kambe. He is deeply motivated by a desire to improve the quality of life for his younger sister, who lives with a disability. This familial responsibility fuels his drive for professional success, though his gambling habits introduce significant financial instability. While not central to major plot arcs, his role involves participating in investigations and supporting colleagues during critical cases, demonstrating loyalty to his team despite occasional interpersonal friction.

Character development remains limited across the series, with no significant evolution in his traits or circumstances. Additional details include his height of 166 cm, a birthday on March 17, a Pisces zodiac sign, and AB blood type.