Taiju Ooki originated in pre-petrification Japan as a high school student. His defining motivation was a five-year, unconfessed crush on classmate Yuzuriha Ogawa. On June 3, 2019, the very day he resolved to confess, a mysterious green light petrified humanity. During the 3,700 years of stone sleep, his intense determination to confess to Yuzuriha enabled him to maintain consciousness alongside Senku Ishigami, a rare feat. He broke free on October 5, 5738. Physically, Taiju possesses a tall, muscular build with spiky brown hair and distinctive vertical stone markings under both eyes. These markings faded after his second depetrification, but he deliberately repainted them. His typical attire is a sleeveless two-piece cloak tied with a rope and primitive boots, though he once wore a lab coat while impersonating a scientist. Taiju's personality blends enthusiastic diligence, profound kindness, and pacifism. He tackles tasks with boundless energy but refuses violence, believing it wrong to harm others even when attacked. This pacifism coexists with remarkable physical endurance; he survived a direct kick from Tsukasa Shishio and traversed 80 kilometers in five hours. His loyalty is unwavering, especially toward Senku and Yuzuriha, driving him to undertake dangerous missions like spying within the Tsukasa Empire. While often perceived as lacking academic intelligence—evidenced by misunderstandings of basic science—he demonstrates practical problem-solving, like enhancing soil fertility with crushed seashells and recalling subtle behavioral cues from Senku. After revival, Taiju collaborated with Senku to develop the revival fluid and rebuild civilization. He infiltrated the Tsukasa Empire as a spy with Yuzuriha, gathering intelligence for the Kingdom of Science. Reunited with Senku, he led the Farming Division and contributed physical labor to projects like underwater statue retrieval and agriculture. His journey extended to global expeditions, including Treasure Island and America, where he faced secondary petrification but retained consciousness again. After a seven-year timeskip resolving conflicts, he married Yuzuriha and supported the moon mission. Key relationships define his arc: his deep romantic commitment to Yuzuriha, guiding his actions across millennia; his steadfast friendship with Senku, assisting him despite limited comprehension of complex science; and his persistent belief in others' inherent goodness, even toward adversaries like Tsukasa. Though not scientifically inclined, Taiju exhibits situational resourcefulness, developed bilingual ability in Japanese and basic English, and an unyielding work ethic. His name, translating to "Big Tree Big Tree" in Japanese, reflects his symbolic role as a foundational support.