Masaru Taniguchi belongs to the G-Boys gang and works at OK Holdings alongside colleague Mitsuki Fujimoto, where approximately twenty other G-Boys members are also employed. His youth was marked by significant delinquency, causing considerable distress to his parents. This changed after moving to Ikebukuro, joining the G-Boys, and securing stable employment—a positive transformation that pleased his family.

His commitment to maintaining this reformed life makes him avoid actions that might jeopardize his standing. This reluctance surfaces when a coworker, after witnessing OK Holdings' connection to a violent assault on another employee, intends to report the company's exploitative labor practices. Following that coworker's complaint, masked attackers wielding baseball bats assaulted them. Despite suspicions linking OK Holdings to the attack, insufficient evidence led to it being classified as random violence. Masaru strongly discourages confrontation, emphasizing the risk of retaliation and potential personal consequences, including financial repercussions for their families.

His fear fully manifests when Mitsuki Fujimoto, overwhelmed by the oppressive environment, attempts suicide by jumping from a building. Masaru is present, tries to intervene, and learns Mitsuki felt trapped by his employment contract and feared penalties against his parents if he resigned. Mitsuki survives due to rescue efforts but is hospitalized. Prompted by this trauma, Masaru resigns from OK Holdings. Shortly after, five masked assailants attack him, resulting in multiple broken bones. He is hospitalized and shares a room with Mitsuki during recovery.

Physically, he possesses black hair and black eyes. His narrative highlights themes of systemic exploitation, the challenges of resisting corrupt power structures, and the personal costs of seeking stability within Ikebukuro's volatile environment.