A boy who identifies as a science lover. He has all kinds of scientific knowledge stored in his head. He will never abandon his friends. He is kind, but will never admit it if pointed out. He always thinks ahead of things. He makes rough calculations and thinks about the details on the spot. His habit is to say "sosonokasu" (to incite/provoke). He calls himself a "mijinko" (daphnia) due to his lack of physical strength, muscle, and fat. He is surprisingly clumsy. A thorough rationalist who will not stick his nose into others' private troubles unless it is a life-threatening crisis, nor will he get angry. Conversely, he will agree if there is a rational reason. He doesn't get flustered even when close to women or seeing them naked. He is determined to save all of humanity from petrification with the power of science. He sees people only as valuable power sources for reviving science. Based in Ishigami Village, he creates a group called the Kingdom of Science and becomes its leader. He always has a cynical and pseudo-villainous attitude. He has an arrogant and haughty personality and does not use polite language with anyone. He has a foul mouth and often makes fun of people, but he never mocks others' efforts. Red eyes. He has a sharp look. His spiky white hair gradually gradients to green towards the tips.

His hairstyle is a black-and-white two-tone. He’s both a magician and a mentalist. With his affable manner of speaking, he usually plays the part of a “shady guy” who seems to act purely out of self-interest. He calls himself the “Bat Man.” Like Senku Ishigami, he’s rather sleazy. In reality, he’s a sentimentalist who pretends to be a realist. At times, he’s a laid-back, cunning strategist with a sharp mind. He reads people’s minds and dominates the room with clever psychological tactics and voice‑imitation skills. Yet when faced with grueling labor or unreasonable circumstances, he can’t help but whine and complain in a half‑tearful, very relatable way—just like any modern teenager. Even in serious situations, he lightens the mood with humor, making him the ultimate mood maker.

He moves swiftly and has sharp eyes. His pupils are a light aqua-green, and he sports thick blond hair tied up at the crown of his head. He is exceptionally decisive and quick-thinking, with a straightforward, justice‑driven personality. He also possesses strong comprehension and can calmly assess situations. As for himself, he pays little attention to minor details, which makes his mannerisms rather rough and often leaves those around him exasperated. He loves talking about romance.

He loves science. Before meeting Senku Ishigami, he used to teach himself, collecting various minerals and experimenting with medicinal herbs. He gathers these items and stores them in a warehouse on the outskirts of the village. He possesses the intellectual curiosity and inquisitiveness essential for scientific advancement. He’s pure-hearted and somewhat naive. He likes to boast about the knowledge he’s acquired, and his cheerful nature shows immediately in his expression and demeanor—making him endearing yet easy to tease. He can’t handle being provoked and tends to blurt out unnecessary remarks. His catchphrase is “Yabe!”

In the world before petrification, he was the heir to the shipping company "Nanami Zaibatsu" which owned the marine-oriented school "Nanami Gakuen." He has loved ships since childhood and collects ship models and bottle ships. In junior high school, he sailed a sailing ship on his own and traveled around the world, calling himself a "professional adventurer." A magnanimous and unrestrained person with great tolerance and excellent charisma. He is rich in emotional expression, but also has a strong nerve, and has never been truly furious in his life. He is a self-centered and overly confident person who asserts that "the world is mine" and has a high-handed attitude, but he is not fixated on his position as a leader; he has no hesitation in working hard himself to obtain what he wants. He also listens carefully to others' opinions, advocates rationality, and does not like to suppress others' will to control them, so he is by no means self-righteous. Regarding his view of women, he has a personal theory that "all women are beautiful, though their types differ," and he does not have a particular disliked type or most favorite type.