Tooru Mutsuki serves as a Ghoul Investigator within the Commission of Counter Ghoul. Assigned female at birth, Mutsuki endured severe physical and sexual abuse from their father during childhood, with their mother failing to intervene. This culminated in Mutsuki killing their family with an axe, though they suppressed these memories and falsely attributed the deaths to a ghoul attack upon entering CCG custody. Within the CCG system, Mutsuki requested to live as male due to profound discomfort with their assigned gender, adopting masculine pronouns, presentation, and a chest binder. Physically, Mutsuki initially appears slim with bronze skin, dark ivy hair, and olive eyes. A permanently active kakugan in their right eye required a medical eyepatch, later replaced by a leather one gifted by mentor Haise Sasaki. After captivity and torture by the ghoul Torso, Mutsuki's hair lightened to white alongside the resurgence of repressed memories. Their hairstyle evolved from a mid-length bob to a pixie cut, then shoulder-length white hair, and finally a short undercut post-Dragon War. Mutsuki's personality began as shy and gentle, hindered by low self-confidence. Anemia and blood repulsion initially hampered their effectiveness as an investigator, fueling inadequacy among peers. Despite this, they demonstrated reliability, fierce loyalty to superiors like Sasaki, and a drive to protect others. Underlying instability triggered violent blackout episodes where they committed brutality without recollection. Following torture by Torso and recovered memories of their family's murder, Mutsuki's psyche fractured, manifesting as ruthlessness, sadism, and arousal during violence. They developed an obsessive fixation on Haise Sasaki, later Ken Kaneki, leading to pathological acts: sexually violating the ghoul Uta while hallucinating him as Sasaki, and repeated attempts to murder Sasaki's wife, Touka Kirishima. Mutsuki declared Sasaki should belong to no one else. Post-Clown Siege and Dragon War, their instability escalated into violent outbursts and near-total mental collapse. As a Quinx, Mutsuki wields ghoul abilities via genetic modification, including a Bikaku kagune for combat and projectile attacks. They exhibit superhuman durability, rapid regeneration, and precise RC cell control evading standard detection. Trained by Juuzou Suzuya in knife combat, they employ quinques like Ifraft, Abksol, and Scorpion 1/56. Post-torture, their combat proficiency heightened, marked by detached cruelty. Relationships define Mutsuki's journey. They revered Sasaki as mentor and confidant, harboring possessive romantic feelings that persisted after Sasaki's CCG defection. Initial friction with Kuki Urie shifted to mutual reliance when Mutsuki aided his mental crisis. A close bond with Ginshi Shirazu involved mediating team conflicts, and Shirazu's death left a deep impact. Interactions with Saiko Yonebayashi remained supportive despite Mutsuki's occasional concern over her work ethic. Narrative parallels link Mutsuki to Juuzou Suzuya through shared trauma and gender ambiguity, and to Karren von Rosewald via cross-living due to trauma. After the Dragon War, Urie guided Mutsuki to confront their actions, eliciting shame and guilt. They subsequently departed Tokyo CCG headquarters, transferring to a rural branch with Shinsanpei Aura and Ayumu Hogi as a tentative step toward atonement. Throughout their arc, Mutsuki's gender identity remains narratively ambiguous, heavily influenced by trauma rather than explicitly framed as transgender.