A beautiful girl with blonde hair and blue eyes. She has a strong sense of justice and speaks with an archaic, stiff tone similar to her father, Kokuyo. While she looks cute and is well-endowed, she possesses the greatest combat ability in the village; even Magma, the strongest man in the village, is no match for her. She has a tomboyish personality, often acting and speaking in direct contrast to her serious and graceful sister, Ruri. She has even boldly changed clothes in front of boys her own age without hesitation. On the other hand, she has a feminine side, such as when her eyes sparkle at the sight of Suika's adorable face. She seems to be somewhat self-conscious about her strength, getting indignant when Chrome calls her a "gorilla" or Senku calls her a "lioness." Surprisingly, she is very expressive and has a wide range of reactions. When Senku tried to use suspicious chemicals to make medicine for Ruri, she approached him with a terrifying expression. Though she may seem reckless and crude at first glance, she is deeply thoughtful and compassionate at her core. Despite being unfamiliar with "science," she judged it to be a technology born of long refinement rather than a suspicious scam based on Senku's dedicated actions. While she doesn't fully grasp difficult logic like Chrome does, she breaks it down and accepts it in her own way. She has a flaw of rushing headlong into danger when her family or friends are in crisis, yet she possesses the coolness to judge "what I can do right now" even in desperate situations without losing herself. She has a habit of starting sentences with "Ha!" when she understands, simplifies, or finds an answer to something. (e.g., "Ha! So in short, I just need to do X.") Her tomboyish nature is closely tied to her sickly older sister, Ruri. Ruri, the priestess who passes down the Hundred Tales to the village, was frail since childhood and was not expected to live to adulthood. Their father, the village chief Kokuyo, ordered Kohaku to succeed as the priestess so the tales wouldn't die out. However, Kohaku rebelled against this. She believed Ruri's sense of responsibility as a priestess was what kept her alive, and if Kohaku took over, Ruri might give up fighting her illness. Above all, Kohaku did not want to be a mere "spare" for her sister's death. To ensure she would never become the priestess, Kohaku acted out as a rowdy daughter unfit for the role. She carried hot spring water every day so her beloved sister wouldn't die, and honed her combat skills so she could protect her. During the Treasure Island arc, as part of an intelligence mission, she was made up with cosmetics through the help of the village beauty Amaryllis and Senku's chemistry. The result, utilizing her natural beauty, was a convincing look for Ruri's younger sister. ...However, in the selection for the inner palace beauties, while Amaryllis and even a cross-dressing Ginro passed easily, Kohaku barely made the cut (she struggled with acting cute).