Taiju Oki, a central figure, begins as a high school student defined by extraordinary physical strength contrasting his limited academic intelligence. Orphaned during childhood under unspecified circumstances, he formed close bonds with Senku Ishigami and Yuzuriha Ogawa. Their shared activities included scientific endeavors like constructing a miniature rocket to deploy stuffed toys into near space and crafting a suit for Senku's adoptive father, Byakuya Ishigami, to pass a space travel swimming test. Taiju nurtured romantic feelings for Yuzuriha for five years but consistently hesitated to confess. On June 3, 2019, as Taiju readied himself to confess to Yuzuriha, a global petrification event transformed humanity into stone. Throughout 3,700 years of petrification, Taiju retained consciousness solely through sheer willpower, driven by his determination to fulfill his promise to confess. Depetrified on October 5, 5738, he awoke to a world where human civilization had entirely collapsed. He soon reunited with Senku, who had been revived six months prior. Collaborating, they developed a revival fluid using nitric acid and alcohol derived from grapes—a concept Taiju proposed. Their first successful revival was a bird, followed by Yuzuriha and Tsukasa Shishio to save themselves from a lion attack. Taiju possesses immense physical strength, stamina, and durability. He can run 80 kilometers in five hours and endure attacks that would incapacitate others, such as a kick from Tsukasa. He served as the primary labor force for Senku’s initial scientific projects, gathering materials and performing demanding physical tasks. Despite his formidable capabilities, Taiju is a committed pacifist who refuses to fight or harm others, even when assaulted, believing in resolving conflicts without violence. Following Tsukasa's betrayal and the formation of the Tsukasa Empire, Taiju and Yuzuriha infiltrated the empire as spies under Senku’s direction, gathering intelligence until the Kingdom of Science secured victory and the factions merged. Within the Kingdom of Science, Taiju led the Farming Division, applying scientific knowledge like using powdered seashells as fertilizer to boost crop yields. His strength and endurance made him vital to the Power Team, undertaking tasks such as underwater statue retrieval without oxygen tanks and restraining powerful opponents like Oarashi. Taiju’s loyalty to Senku and Yuzuriha is unwavering. He consistently prioritizes their safety, shielding Yuzuriha during the petrification event and offering to sacrifice himself for Senku during the lion attack. Though initially unable to confess his feelings due to concerns about pressuring Yuzuriha in their precarious situation, their relationship progressed gradually. They married after the successful completion of the moon-landing project. Despite frequent characterization as unintelligent—evidenced by suggestions like finding calcium carbonate in a gym storeroom or claiming cellphones as civilization’s most important tool—Taiju demonstrates practical problem-solving. He recalled scientific concepts Senku taught him, such as using shells for soil enhancement, and successfully masqueraded as "Dr. Taiju" to deceive Dr. Xeno. He also exhibits strong mental resilience, remaining conscious during a second global petrification event and contributing to long-term missions like the voyage to America. His appearance includes a muscular build, spiky brown hair, and distinctive vertical petrification scars on his face, later replaced with paint after his second depetrification. He typically wears a sleeveless cloak tied with a rope and primitive boots, though he adopted modern clothing and a lab coat during his scientist impersonation.