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 is turned out to be the savior the village ancestors talk about, 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 delicate/complicated work it takes to make modern inventions, Kohaku often teams up with Chrome to scavage ingredients and "persuade" Kinro and Ginro to help with the labor.
Kohaku is a young woman of average height with a slim-but-curvy figure, a delicate face, blue eyes, and blond 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 heritage as the descendant of Byakuya Ishigami and Lillian Weinberg. She shares a resemblance with her older sister, Ruri, but has wild hair in comparison to her sister's soft, flowing hair, and a slimmer body. Her clothing consists of a crude, navy blue dress with a rope tied in the middle, and uniquely shaped stone sandals.
Kohaku is a kind young woman, caring deeply for her sickly older sister, willing to participate in the tournament for her hand in marriage just to protect her. This care extends to her comrades, and anyone she's loyal to. She was willing to lie and take scolding in order not to reveal she was attacked by Tsukasa as not to distress her sister and the villagers.
In addition to this, she has a reckless and hotheaded personality, often reacting in anger to being called a gorilla or lioness due to her strength and physicality. She also acts on her emotions at times, going against rational thought and rushing in. Kohaku also has a bit of a teasing side, asking Chrome if he could fall for her to her resemblance to her sister.
She's repeatedly impressed by Senku's scientific creations, although at first, it took her a while to accept that it's not simply magic.
Kohaku excels at fighting, hunting, and general survival skills. She is a tomboy by nature, having little interest in more typical feminine activities and has little knowledge about them, although she does seem to enjoy some lavish clothing that was provided to her. Kohaku has no problem with being around boys while swimming or changing clothes; she will, however, retaliate if a boy stares lustfully at her breasts. She possesses a sharp instinct and intellect.
During the early part of the story, Kohaku tends to be a hair-trigger away from attacking people she distrusts. Such was her first impression of Gen, who admitted to being initially a spy for Tsukasa; she even attacked Tsukasa himself without really knowing why he attempted to kill Senku. She also possesses a strong sense of justice, which in pair with her hotheadedness leads her into dangerous situations such as her battle with a more competent fighter like Tsukasa.Thanks to Senku's numerous scoldings and encouragement to think more than one step ahead, Kohaku grows out of this habit, but her temper is still a problem.
Perhaps because of her instinct, Kohaku seems to be a good judge of character. She was able to deduce that Gen was the kind of person who, despite being able to lie without batting an eye and claiming to only work for his self-interest, cherished his loyalty and friendship with Senku. She also recognized that Chrome was in love with Ruri, but hadn't realized his own feelings yet, and was able to read Senku's personality to an extent.
Similar to Senku, she doesn't seem to be interested in romance, previously claiming to have fallen for Senku when she meant that she found him interesting as a person. It was stated that she had feelings for Chrome in some ways, she asked if Chrome would accept her as his wife as she and Ruri look alike. She has shown to hate shallow or selfish men, at first disliking Gen for wanting to switch to Senku's side due to the apparent benefits switching would reap. However, Kohaku later describes the kind of man she's into: "Men, who for what they believe in, will keep putting one foot in front of the other, for all eternity, chipping away at progress." This indicates along with several small moments, including hugging Senku when freed from her petrification that she does in fact harbor feelings for Senku, but is pragmatic enough to not act on them for the moment, preferring to do what she can to further the restoration of humanity and the defeat of Why-Man.
Abilities and SkillsEnhanced physical prowess: Kohaku appears to be well known in her village due to her combative abilities, as both Kinro and Ginro were afraid of her. Tsukasa, a world-class fighter, stated that she would have been famous for her fighting abilities back in the Pre-Petrifaction world. Kohaku possesses great strength and endurance, credited by Chrome to be one of the few superhumanly strong individuals within the village. being able to carry a heavy pot filled with hot water on a daily basis for her sickly older sister, Ruri. In an extra, Kohaku rates herself with 1000 battle points, Kinro having 500 and Ginro having 100 respectively. Despite her skill, she is inferior to Tsukasa Shishio, Hyoga, and Mozu.
- Enhanced strength: She is tasked with carrying a heavy pot filled with hot water over long distances on a daily basis for her sickly sister Ruri, Senku noting it's just shy of 50 kilograms (which is around 110 pounds). When Senku tries to lift the pot in order to help Kohaku, he quickly succumbs to its weight.
- Enhanced speed: Her more notable traits are her speed and agility, which makes her highly proficient in close-quarters combat. When fighting, she attacks with a flurry of blades and kicks. She also possesses quick reflexes, as she was able to easily stop an attack from Kinro and Ginro when they both attacked her.
- Enhanced senses: In addition to all this, Kohaku is gifted with incredible eyesight. She first noticed something is off about the North Star not being true north, being able to spot Tsukasa and Senku from afar, and finding oil from just the aerial view of the hot air balloon and a map. However, she was unable to sense Kirisame in their first fight. Matsukaze even blitzed right through her, without her noticing.
Hunting: Kohaku is an accomplished hunter. She caught a wild boar for Francois with ease when they were looking to capture some for their farm. She's one of the most reliable people when it comes to hunting. Additionally, her extraordinary eyesight helps in all these endeavors.
Instinct: Perhaps because of her experience in hunting, Kohaku possesses a sharp instinct, able to discern information and situations correctly.
Intelligence: While not as smart as Chrome or skilled as Kaseki, she proves to be quick on the uptake in understanding of some of the science Senku demonstrates, and the complex strategies they use in their endeavors, like her covert acts to send Senku supplies and critical information despite the lack of 2-way communication and her illiteracy. She also used a coded word to get her allies' attention, during an enemy attack., When Ginro was severely wounded, she realized that in order to save him, she would have to petrify him.
Kohaku wields two primitive-looking knives and an orange-colored buckler. Later, she discards her dual knives in favor of the katana that Kaseki and Senku forged for her and the other warriors.
- Her name Kohaku is the Japanese word for Amber, which is also a fossilized tree resin.
- In the cover of Chapter 17, her eyes were mistakenly shown as yellow/brown, even though it was stated that she has blue eyes. This mistake was later fixed with the cover of Chapter 22.
- Kohaku ranked 2nd in the 1st Character Popularity Poll.
- She was close to rivaling with Gen, who ranked third place.
- She is the first girl to kiss Senku.
- Kohaku only hits Chrome for calling her a gorilla, even when Senku does the same.
|Male||Taiju Oki • Senku Ishigami • Gen Asagiri • Chrome • Kaseki • Kinro • Ginro • Magma • Kokuyo • Ryusui Nanami • Matsukaze • Tsukasa Shishio • Hyoga • Mozu|
|Female||Yuzuriha Ogawa • Ruri • Kohaku • Suika • Nikki Hanada • Minami Hokutozai • Kirisame • Homura Momiji|
|Male||Chrome • Ginro • Jasper • Kaseki • Kokuyo • Kinro • Magma • Mantle • Soyuz • Tetsuken • Ibara • Mozu • Oarashi • Matsukaze|
|Female||Garnet • Kohaku • Ruby • Ruri • Sapphire • Suika • Shirogane • Shovel • Turquoise • Amaryllis • Kirisame|