"I'll leave the thinking part to you, Senku. So you rely on me for the physical part!"
— Taiju Oki, Dr. Stone, Chapter 1
Together with Senku, he nobly aspires to rebuild the lost human civilization by depetrifying everyone caught in the phenomena that happened 3,700 years ago.
Under Senku's planning, he joins the Tsukasa Empire as a spy to help bring him down. After rejoining the Kingdom of Science, he is placed on the Power Team and usually puts his inhuman amounts of endurance to good use with assistance in building things, farming and gathering.
Taiju is a muscular young man with spiky brown hair, thick eyebrows, and two horizontal stone markings, one of which starts at his hairline above his left eye and reaches down underneath it, and the other one located under his right eye. The markings were later removed after his second revival and replaced with identical ones drawn with paint. He wears a 2-piece, sleeveless cloak that reaches past his knees and is tied together with a rope, and primitive boots.
After his second revival, his scars disappeared and he soon adorned war paint in reflection of his stone markings, during Tsukasa's revival.
When posing as Dr. Taiju, he wore a lab coat over modern clothing to play the part.
Taiju is an outgoing, friendly, and kind person. He's enthusiastic about performing even small tasks and a diligent worker. He is very determined when something is important to him. He tends to yell loudly and is enthusiastic regardless of the task so long as he proves useful. He is persistent and determined. Despite being emotional and expressive, he has great control of his temper, never losing his cool or acting impulsively. He is notably one of the kindest people in the series, refusing to murder Tsukasa and wanting to find peaceful solutions without murder or hurting others as evidenced by his pacifistic nature. He has a straightforward and honest nature, refusing to take a love potion that Senku claimed would make him irresistible and stated he would confess to Yuzuriha on his own. In addition, he tends to easily trust others and believe in the good of others, believing Tsukasa to be a good person when they first met for wanting to eat the meat of a lion he killed as not doing so would be disrespectful of the lion's death. Even after becoming enemies and witnessing him "murder" Senku, he shows no rage or anger despite greatly mourning his friend's "death," instead wishing Tsukasa a benign farewell.
He loves Yuzuriha, although he couldn't bring himself to confess his feelings for five years. It was his drive to finally tell her how he feels that allowed Taiju to remain conscious during his several thousand-year petrification. Even after they are de petrified, he has yet to confess his feelings because he does not want her to feel pressured to answer how she feels when he believed they were some of the only few humans remaining. He also refused to de-petrify her until after clothing her, proving to be a gentleman and considerate of the feelings of others. He is a loyal friend and person to those he cares for, placing great trust in Senku and being deeply loyal to Yuzuriha, continuously willing to put his life on the line for the two of them.
He greatly admires his best friend Senku, even though he only has a limited understanding of scientific practices. He gets easily impressed by Senku's inventions and he assists Senku with his experiments by providing the manpower necessary for them. Taiju was willing to sacrifice himself in order to let Senku escape from a pride of lions, further attesting to his kindness and selflessness.
Despite his massive strength, he is a pacifist who refuses to fight others because he does not want to hurt others. He once even offers to let Tsukasa smack him until he is satisfied in the hopes of deterring him from destroying anymore petrified humans. Nonetheless, he has the endurance and patience to complete any task no matter how arduous.
While considered book dumb and not good with science, it is shown that he is capable of finding mundane solutions without science and can apply the science and knowledge Senku imparts on him and use it to his advantage, such as remembering how Senku stated that shells were good for upgrading soil for farming and applying it to his fields, which allowed it to grow in contrast to Yo's and Magma's fields. He can be resourceful and also has a good memory, managing to remember that, in the past, Senku did not have the habit of cracking his neck and figuring out it was a code from Senku. He also knows his limitations and what he is good and not good at without overestimating himself.
Abilities and Skills
Enhanced physical prowess: Taiju possesses an extremely sturdy body, something his friend Senku vouches for. He is strong enough to restrain Oarashi, who previously threw off Magma and Kinro at once.
- Immense durability: He is the first human to be able to withstand a kick from Tsukasa without immediately losing consciousness, opening his eyes as soon as Tsukasa leaves with Senku, saying he needs no recovery at all. He took a hit from Mozu, while earning praise for his endurance.
- Immense stamina: He also possesses immense stamina, able to cross 80 kilometers in 5 hours. Gen Asagiri has also noted that his stamina is immense. He is also the strongest man for endurance after Tsukasa was put in cryosleep and Hyoga was incarcerated. Magma, Ginro, and Yo notably respect Taiju due to his perk of "limitless stamina" that surpasses even the strongest man in Ishigami Village.
- Enhanced strength: Taiju, besides his sturdiness, is also considerably strong. He was able to hurl a huge boulder at Tsukasa's location high enough to make it fall not before Tsukasa kicked the gunpowder to spread it in order spark an explosion. He is strong enough to restrain Oarashi, who previously threw off Kinro and Magma with little effort.
Mental resilience: Besides Senku, he remained awake while petrified because of his strong willpower and desire to confess to Yuzuriha.  Working in pair with his stamina and personality, Taiju has an unyielding amount of determination, and will complete his task no matter how arduous or long it is. Even at the face of his friend's death, he refuses to believe Senku's fate and through perseverance, eventually finds the key to reviving him. Dr. Xeno makes a remark that only a very small number of humans can hold their conscious together for 4 millennia, doubting that the entire Perseus group are "mental champions of the highest order".
Bilingualism: Taiju speaks Japanese and English. He was initially unable to understand Senku and Ukyo. Later on, he is able to understand Dr. Xeno when he switches over from Japanese to English on the radio.
Low intellect: For a high schooler, Taiju is incredibly unintelligent. He mindlessly suggested that calcium carbide Senku was looking for could be found in gym storerooms, despite most of the buildings being completely demolished by the passage of time. He also comically suggested that the most important tool for civilization is a cellphone. Taiju is shown to possess below-average logic and knowledge, easily on par with the Ishigami Villagers (minus Kaseki and Chrome) in how little scientific knowledge he possesses. For example, at one point, he thought the base component for gunpowder would be fireworks (it's the other way around). It is safe to assume Taiju did poorly on tests and was probably held back a few school years back in the Pre-Petrification World. Nevertheless, Taiju has his bright moments, such as suggesting that Senku and he make wine through grapes that he found earlier. He also possesses some knowledge in farming thanks to Senku.
- Taiju's name is composed of "tai" (大 big; large) and "ju" (樹 tree) to create Taiju (Big Tree), while Ōki is composed of "ō" (大 big; large) and "ki" (木 tree) to create Ōki (Big Tree).
- This means that his name is literally "Big Tree Big Tree".
- Taiju shares a motif with Senku and Yuzuriha in that his name contains "ju" (樹 tree) and "ki" (木 tree) in his name, which correlates to the theme of "land, sea, and sky".
|Male||Taiju Oki • Senku Ishigami • Gen Asagiri • Chrome • Kaseki • Kinro • Ginro • Magma • Kokuyo • Ryusui Nanami • Matsukaze • Tsukasa Shishio • Hyoga • Mozu • Yo Uei|
|Female||Yuzuriha Ogawa • Ruri • Kohaku • Suika • Nikki Hanada • Minami Hokutozai • Kirisame • Homura Momiji|
|Male||Byakuya Ishigami • Gen Asagiri • Hyoga • Ryusui Nanami • Senku Ishigami • Shamil Volkov • Taiju Oki • Tsukasa Shishio • Ukyo Saionji • Yakov Nikitin • Yo Uei|
|Female||Connie Lee • Darya Nikitina • Homura Momiji • Lillian Weinberg • Nikki Hanada • Yuzuriha Ogawa • Minami Hokutozai • Mirai Shishio|