Kinji Tohyama is a 17-year-old Japanese male with wavy black hair, brown eyes, and an average build, standing 170 cm tall and weighing 63 kg. Born on July 16, 1991, under the Cancer zodiac sign with blood type A, his lineage traces back to Edo-period police chief Kagemoto Tohyama (Kinshiro). His immediate family includes his deceased father Konzou Tohyama, an unnamed deceased mother, a stepmother, his deceased older brother Kinichi Tohyama, younger brother Kinzou Tohyama, half-sisters Kaname and Kanade Tohyama, sister-in-law Patra, and paternal grandparents Magane and Setsu Tohyama. Raised by his older brother Kinichi after their parents' deaths, Kinji mastered the Tohyama family combat techniques and inherited the genetic Hysteria Savant Syndrome (HSS). Childhood visits to the Hotogi Shrine led to a friendship with Shirayuki Hotogi; he often secretly took her outside despite potential punishments. Middle school trauma occurred when female classmates, including Kikuyo Kagataka, exploited his HSS—activated by sexual arousal—to force him into being their "personal ally of justice." After attempting to stand up for himself, he faced group retaliation, resulting in lasting distrust of women and an aversion to using HSS. Initially enrolling in Tokyo Butei High's Assault department, Kinji achieved S-Rank status during the entrance exam by capturing all other candidates and defeating five instructors under HSS influence, forming the "Golden Duo" partnership with Reki. When his brother Kinichi was falsely reported dead and publicly ridiculed for a failed mission, Kinji grew bitter toward the Butei profession. He transferred to the Inquesta department, let his rank drop to E, and planned to quit for a normal life. His resolve faltered after Aria H. Kanzaki saved him from the "Butei Killer" bomber, enlisting him as her partner to clear her mother's name. Kinji's personality is cynical, antisocial, and sarcastic, especially around women, stemming from his past. He rarely smiles, maintains a stoic demeanor, and often acts as the straight man to eccentric peers. He harbors a strong inferiority complex, initially rejecting his family legacy in favor of ordinary civilian life. This desire is challenged by figures like the Cao Cao sisters, who assert his HSS makes coexistence with "normal" people impossible. After briefly transferring to a regular high school, he found civilian life unfulfilling and returned to Butei High, though he continued to disdain its culture. His defining trait is Hysteria Savant Syndrome, which triggers through sexual arousal (e.g., physical contact or kissing). In this state, his physical strength, reflexes, speed, and cognitive abilities increase thirtyfold, enabling superhuman feats like deflecting bullets with knives or fingers, moving at supersonic speeds (Ouka technique), and rapid analysis. HSS also shifts his personality into a chivalrous, seductive protector of women, often causing embarrassment afterward. A secondary "Hysteria Berserk" state emerges when women close to him are threatened, unleashing suppressed rage. Kinji's combat style employs firearms and close-quarters techniques. His primary weapons are a modified Beretta 92FS Inox ("Kinji Model") capable of three-round bursts or full-auto fire, a butterfly knife from Kinichi, a similarly modified Desert Eagle Mark XIX, and a seax named Ragnarok inherited from Sherlock Holmes. He later earned the title "Quadra of Mimicry" for dual-wielding both guns and blades simultaneously. Kinji's relationships are complex. With Aria Kanzaki, he evolves from reluctant partners to mutual romantic interests, though he often downplays his feelings. His HSS activates more easily around her, sometimes via minor provocations, and he gives her a ring she misinterprets as a marriage proposal. Shirayuki Hotogi, his childhood friend, is obsessively devoted, but he finds her clinginess irritating despite occasional hidden affection. Riko Mine exploits his HSS for her schemes, while Reki respects his leadership. He later formed Team Baskerville as its leader, with Aria as vice-leader and Shirayuki, Riko, and Reki as members. Throughout the series, Kinji confronts his brother Kinichi, who resurfaces with the antagonist organization IU. After defeating him to protect Aria, Kinji urges him to find non-destructive methods against IU. Post-graduation, he retired from active Butei work and established the militant company Tohyama Warrior Office to retain his Butei license. Eventually, he stepped down to focus on college entrance exams, signifying a partial reconciliation with his extraordinary life while retaining his core desire for normalcy.