Kohaku descends from modern humans Byakuya Ishigami and Lillian Weinberg, giving her American-Japanese heritage. She is the younger daughter of Kokuyo and sister to Ruri in Ishigami Village; her mother died during her childhood. Kohaku refused the village priestess role, fearing it would weaken Ruri's will to live, and deliberately adopted wild behavior to seem unfit. Physically, she has blonde hair typically in a spiky ponytail, blue eyes, and stands 160 cm tall. Her usual attire is a practical sleeveless navy blue V-neck dress with traditional Japanese undergarments and stone sandals. A tan ribbon choker around her neck mirrors Lillian's. Her appearance adapts functionally or seasonally, like wearing winter furs or a party dress on the voyage to America. In the spin-off *Dr. STONE: 4D Science*, she briefly cuts her ponytail, though it regrows quickly. Kohaku's personality is fiercely protective of loved ones yet impulsive and prone to rage when provoked. She prioritizes others' safety, lying about Tsukasa's attack to avoid distressing her sister and villagers. Her loyalty is unwavering once trust is earned, though she initially threatens untrusted individuals like Gen. She struggles to control her temper, especially when allies are endangered, leading to reckless actions like attacking Tsukasa after Senku's apparent death. Despite her combat skill, she admits an inability to kill unless ordered, seeking external validation for such acts. She enjoys physical activities like hunting, swimming, and snowboarding, and shows playful interest in romance, teasing others while observing romantic developments. She reacts negatively to insults about her femininity like "gorilla" or "lioness," yet values practicality over possessions and uses elaborate, occasionally archaic language that sometimes causes misunderstandings. As Ishigami Village's strongest warrior, Kohaku possesses exceptional physical abilities: 11.0 eyesight, remarkable agility, and proficiency with stone daggers and swords. She leads the Kingdom of Science's "Power Team" for combat and labor. Though initially apathetic toward science, she gradually develops observational skills useful to scientists, like identifying corn debris to locate resources. Post-conflicts, she joins a police unit focused on teaching self-defense and maintaining order. Relationships are central to her development. Deep care for Ruri motivates her initial alliance with Senku to obtain medicine. After Senku saves her from a felled tree during her fight with Tsukasa, she becomes one of his most loyal supporters. She acts as a protective older sister figure to Suika and maintains a teasing dynamic with Chrome, encouraging his romantic pursuits of Ruri. Romantic advances from Ginro, Magma, and Ibara are dismissed, though she displays occasional affection toward Senku, including a distraction kiss on Treasure Island and a reunion hug in the New World arc misinterpreted by others. Throughout the series, Kohaku participates in critical missions: escorting Senku to Ishigami Village, infiltrating Treasure Island's harem selection, and voyaging to South America aboard the *Perseus*. Her growth includes adapting to scientific methods like radar technology and contributing to agriculture. Later, she aids in establishing New America City and prepares for lunar exploration, consistently balancing combat readiness with emotional support for allies like Mirai Shishio.