Tooru Mutsuki serves as a Special Class Ghoul Investigator for the Commission of Counter Ghoul (CCG). Initially part of the Quinx Squad under Haise Sasaki's leadership, Mutsuki later undertakes temporary assignments with the Hachikawa and Suzuya Squads during major operations. After leaving the Tokyo Special Countermeasures (TSC) unit, Mutsuki transfers to a rural branch office alongside colleagues Shinsanpei Aura and Ayumu Hogi. Known by the nickname "Eyepatch" due to a medical device concealing a permanently active kakugan in their right eye—later replaced by a leather eyepatch gifted by Sasaki—Mutsuki wields a bikaku-type kagune and utilizes quinques including Ifraft, Abksol, Black Linshing Nut 16/16, and White Loosting Nut 16/16 in combat. Physically, Mutsuki presents as slim with bronze skin and green eyes. Early depictions show dark ivy-colored hair in a mid-length bob, which lightens to white over time as their build becomes more athletic. Hairstyles evolve further: a pixie cut follows promotion, shoulder-length white hair appears after regaining suppressed memories, and finally a short nape undercut after the Dragon War. Mutsuki typically wears formal attire with a white trenchcoat and a chest binder. Significant scars mark their upper left pectoral and right side, remnants of past trauma. Mutsuki endured severe childhood trauma in an abusive household dominated by their father, suffering physical violence, near-drowning, and sexual harassment while their mother remained passive. At age 12, during a dissociative episode, Mutsuki killed their entire family with an axe but retained no memory, insisting a ghoul was responsible. Placed in CCG custody, Mutsuki requested to live as a man and adopt masculine pronouns. At the CCG Academy Junior School, they faced bullying and rumors about animal mutilation, later confirmed to be acts encouraged by instructor Goumasa Tokage. Personality-wise, Mutsuki begins as gentle, kindhearted, shy, and insecure, struggling with low self-esteem, anemia, and blood repulsion, which hampered effectiveness as an investigator and fueled frustration. Despite this, they demonstrated reliability, diligence, and a protective instinct. Mutsuki later develops assertiveness and takes on active coordination roles. However, they suffer dissociative blackouts where a violent alternate personality emerges, capable of extreme acts like necrophilia or mutilation, as seen in the revenge killing of their torturer, the ghoul Torso. These episodes escalate after the Clown Siege, leading to obsessive behavior toward Haise Sasaki (later Ken Kaneki), intense jealousy toward Touka Kirishima, and unstable violence against civilians associated with Touka. Key relationships shape Mutsuki's path. They harbor profound loyalty and a secret romantic obsession toward Sasaki; his defection elicits no ill will but intensifies Mutsuki's fixation, culminating in delusional violence against perceived rivals like Touka. Within the Quinx Squad, friction occurred with Kuki Urie over differing attitudes toward Sasaki, though they later cooperated closely. A supportive friendship existed with Ginshi Shirazu, whom Mutsuki counseled on leadership, and they mediated with Saiko Yonebayashi during investigations. Mutsuki mourned Shirazu deeply after his death. They also mentored Shinsanpei Aura, who later covered for Mutsuki's violation of Uta's corpse during a dissociative episode. Mutsuki's story arcs include pivotal investigations. Capture and torture during the Torso case triggered the resurgence of repressed memories and violent tendencies. The Ghoul Auction Operation saw Mutsuki unlock their bikaku kagune, enhancing combat skills. During the Rushima Landing Operation, mental deterioration manifested in pronoun fluctuations ("ore" to "watashi") signaling identity instability. Post-Dragon War, Mutsuki appears more composed, adopts simpler white clothing, and stabilizes their kakugan. Their final trajectory involves leaving the TSC for work in a rural branch.