Kohaku originates from Ishigami Village, born millennia after the global petrification event. She is the younger daughter of Kokuyo and sister of Ruri. Her mother died during Kohaku's childhood. When Ruri fell gravely ill, Kohaku shouldered daily tasks like fetching hot spring water to sustain her sister. To shield Ruri from losing purpose as priestess, Kohaku deliberately defied her father's wish for her to assume the role, adopting a wild persona to avoid the position. Kohaku embodies bravery, a strong will, and directness, often using traditional speech patterns starting with "Ha!" She displays fierce loyalty, honesty, and swift protectiveness towards loved ones, though reacts angrily to nicknames like "female gorilla" or "lioness." Despite a boyish demeanor, she cares about perceptions and shows moments of girlish embarrassment, such as encountering nudity. She deeply admires those pursuing ideals with unshakable determination, indirectly citing Senku's scientific perseverance as her ideal. Holding renown as her village's strongest warrior, Kohaku possesses exceptional physical abilities. Her exceptional 11.0 vision grants near-superhuman visual acuity. She combines remarkable speed, agility, and combat proficiency with weapons including stone daggers, katanas, and spears. Her combat record includes frequent losses against major opponents like Tsukasa, Hyoga, Homura, and Kirisame. These defeats create opportunities for Senku's scientific interventions, exemplified when Gen sabotaged Hyoga's spear to save her. Her path crosses with Senku after witnessing Tsukasa's attempt to kill him. Though initially overpowered and trapped under a tree by Tsukasa, Senku rescues her using an improvised pulley. Grateful, she pledges loyalty and guides him to Ishigami Village. She becomes vital to the Kingdom of Science, leading its Power Team and contributing to critical missions. Her tasks span manual labor—transporting heavy water or sulfur—to combat support, like using Kinro's spear as a lightning rod for magnet creation. She aids in synthesizing sulfa drugs to cure Ruri, collects invention materials, and participates in reconnaissance, including a disguised infiltration during the Treasure Island arc. Kohaku's relationships drive her actions. Devotion to Ruri motivates her early efforts, while trust in Senku anchors her role in the Kingdom of Science. She develops bonds with allies like Chrome, whom she teases but respects, and Suika, whom she fiercely protects. After the main conflicts, she joins a police force alongside former adversary Homura Momiji, teaching self-defense and maintaining village order. Throughout her journey—battling Tsukasa's empire, exploring continents, confronting the petrification threat—Kohaku proves resilient and adaptable. Her character arc shifts from village guardian to defender of scientific progress, culminating in a role focused on societal stability.