Jin Kaito is a Japanese male with black hair and brown eyes. He works full-time as a gigolo, a profession he entered after leaving university. Jin scours the city for potential female clients, prioritizing attractive women. This work carries high risk; refusing gang affiliation forces constant vigilance against attacks from enforcers and thugs. Despite these threats, he maintains a consistently relaxed, carefree attitude, largely unaffected by the danger.

At 22, Jin accepts a challenge from Ai Mizushima to make her "scream with pleasure," lured by the prize of a new sports car; this wager drives his primary narrative. During this time, he becomes entangled with yakuza factions, encountering a female assassin seeking vengeance for her family's murder. Jin lacks decisive agency in these conflicts, often relying on others to survive, including a female companion rescuing him from violence.

His personality centers on projecting a cool, self-assured image, frequently using smooth-talking phrases reminiscent of pulp fiction. His roguish charisma proves consistently appealing. However, this persona masks his vulnerability in confrontations, where he frequently suffers beatings and requires external protection.

Jin shares a home with Ranko, identified as an ex-girlfriend. Their cohabitation includes casual physical intimacy. Later, after his gigolo work deteriorates—marked by unsuccessful client interactions and financial exploitation by a yakuza-affiliated woman—he reunites with Ranko. Though she expresses a desire for a stable, honest life together, Jin demonstrates no substantive lifestyle changes or personal growth, maintaining his established patterns.