Kazushi Yamagishi, a middle school friend of Takemichi Hanagaki, emerges during the protagonist’s first time leap. His chestnut hair—often tied back—and grape-colored eyes shift across timelines, evolving from mid-length tied bangs in youth to slicked-back styles with silver glasses, earrings, a goatee, and a left eyebrow scar in alternate realities. Known for excitable loyalty, he masks self-doubt by feigning unintelligence, convinced glasses enhance his intellect. Contradicting this facade, his encyclopedic grasp of delinquent gangs earns him monikers like "Gang-Dex" and "Walking Delinquent Encyclopedia," enabling allies to navigate hidden threats like Kiyomasa’s plot against Draken.

A founding member of the Mizo Middle Five and later captain of Tokyo Manji Gang’s First Division Strike Squad, Kazushi fights in pivotal battles against Tenjiku and Shion Madarame. Though not a top-tier combatant, he endures clashes, balancing tactical loyalty with a distaste for violence. His strategic influence surfaces in naming the "Bloody Halloween" conflict, cementing his role in shaping gang mythology.

Across timelines, Kazushi’s motivations stay anchored in shadowy manipulation of delinquent networks, prioritizing information over direct conflict. He frequents Takemichi’s home, underscoring their bond, and maintains quiet persistence in flashbacks and alternate arcs. His name—"one officer" (Kazushi) and "mountain shore" (Yamagishi)—hints at layered identity, while trivia highlights his rumor-loving nature and glib conversational skills. Despite evolving aesthetics, core traits endure: loyalty, tactical insight, and a blend of self-deprecation and niche brilliance.