Kohaku is a young woman who is a descendant of modern humans. She is Ruri's younger sister and the daughter of Kokuyo. She is one of the protagonists of the series. After meeting Senku and witnessing his bravery, courage and talent, Kohaku invites him to her village. Since Senku assists and fascinates the village with many of his scientific inventions and turned out to be the savior the village ancestors talk about in the stories that are passed down, the population is ultimately rallied to fight and stop Tsukasa's tyrannic empire. After Taiju, Kohaku is the most loyal to Senku. Since learning about science, and the delicate, complicated work it takes to make modern inventions, Kohaku often teams up with Chrome to scavenge ingredients and "persuade" Kinro and Ginro to help with the labor. Kohaku is a young woman of average height with a slim figure. She has a delicate face, blue eyes, and blonde hair tied-up in a spiky ponytail. Her appearance is that of someone who appears to be a mixed heritage of American/Japanese, denoting her as the descendant of Byakuya Ishigami and Lillian Weinberg. She shares a strong resemblance with her older sister, Ruri, but has wild hair in comparison to her sister's soft, flowing hair, and a slimmer body. Her most typical attire consists of a V-neck, sleeveless and short navy blue dress. Underneath she wears makeshift garments akin to a bra and a fundoshi (traditional Japanese garment). The dress is tied with a rope tied in the middle, and uniquely shaped stone sandals. She also wears a tan ribbon as a choker around her neck, which resembles the one worn by Lillian as well. She has a different fur dress and footwear for the winter, and occasionally takes on different outfits, either for functional reasons (such as the dresses she wore in Treasure Island) or out of her own volition, such as the party dress she wore while helping Senku gamble against Ryusui and Gen on the trip to America. Her wooden shield is eventually replaced with a metal lined one made by Senku. Kohaku is a kind young woman, willing to put her sweat and tears, as well as her own life on the line to protect those she holds dear, taking rigorous care of her sickly older sister, and even willing to participate in the tournament for her hand in marriage just to protect her. She purposefully lied and took a scolding in order not to reveal she was attacked by Tsukasa, as not to distress her sister and the villagers. She is just as caring towards her friends and comrades, being particularly dedicated to Suika, playing for her the role of an older sister herself. Furthermore, Kohaku is always attentive to give emotional support to people going through hardship in general, such as Mirai upon the loss of her brother. She can sometimes be seen thoughtfully worried for people, in which cases she tends to sit down with her arms around her thighs, if there is nothing more she can do to help. On her flip side, she tends to be extremely cautious or even threatening with people who haven't earned her trust. Gen was subjected to this for a rather long period of time, with multiple threats on his life from her, and even Senku found himself in a similar standing early on. After he interpreted her words as her confessing to having a crush on him upon being rescued, she would not dare fall asleep near him without her knives firmly grasped. It should be noted that if she feels safe instead, she will fall asleep basically anywhere and in any situation. To further complicate the matters, she has a choleric and impulsive personality that makes her burst in rage or carry out reckless actions if provoked, which could potentially lead her into fatal mistakes. While she could be daring in general, usually it took some rather specific scenarios to send her on a blind rage, most typically having her friends be captured by an enemy. People such as Senku, Gen and Kokuyo have made attempts to wrangle these uncontrollable reactions, with varying degrees of success. Despite their efforts, she makes little to no improvement; however, as the story progresses, she encounters much fewer of the situations that would have pushed her over the edge, as she spends most of the time not separated from her group of close friends. In less dire situations she is able to make conscious decisions, but that can still go poorly given the parade of new dangers she doesn't understand, either from unexplored nature or new people, as well as her own subjective decisions informed by her strong sense of justice and bad temper. This volatile combination tends to bring her into dangerous situations such as her battle with a more competent fighter like Tsukasa, whom she decided to attack after witnessing him taking Yuzuriha hostage and then killing Senku, not being concerned with whichever motives he might've had. Despite how violent she can be, Kohaku has admitted that she could not bring herself to kill a person, and if she were to do it, she would have to do it under orders, diminishing her responsibility in the act. This is not without precedent, as whenever she threatened to explicitly kill someone prior to this admission, it could be observed that she often sought the approval of someone else. One example was when Gen admitted to be a spy for Tsukasa, she asked Senku if she should dispose of him. Prior to this, when Gen first showed up at the village, she instead shifted the decision onto Gen himself, by leaving up to him whether she should kill him or not, based on his choice for his next move.