When the twin demons Lechku & Nechku cause a deadly blizzard in Kamui, Oki stole the sacred sword of the Oina tribe. He fights lesser demons in order to make his sword glow silver with the power to stop the twin demons.
Oki is very naive and only thinks about how to improve his strength with the sword. He believes he is the only one that can save his tribe from the demons, and does not want to be helped by either Amaterasu, Issun or any of his own kind.
Oki seems to have a minor rivalry with Samickle, or at least that's what Samickle likes to believe, since he thinks of Oki as acting without thinking. They warm up to each other once the twin demons have been slain, and Oki's eyes have opened for kindness, help and friendship.
When Amaterasu first arrives in Kamui, there is a harsh blizzard raging throughout the land. Issun tells her to seek out shelter until the blizzard calms down a bit. She finds a home nearby and goes inside, relaxing near the fire. Shortly after, the owner, Oki, takes offense and threatens Amaterasu with his sword, Kutone. They circle the fire slowly, watching each others' movements. When Oki is near the doorway, he gestures to Amaterasu to take the fight outside and waits for her. When she joins up with him, they battle against each other, Oki using both his human and wolf forms.
After the fight, he commends her and knows that she is not a normal wolf. He then informs both her and Issun about Kamui's situation regarding the twin demons Lechku and Nechku, the cause of the blizzard. He also tells them about a prophecy, which is: "The wall of ice shall shatter and open the way to the heavens, when Kutone, the guardian sword, glows silver." He interprets it that he must slay monsters until the sword glows, which will rid Kamui of the blizzard.
Later on, it is revealed that Oki stole Kutone from the village Wep'keer so that he alone can defeat the demons. When Amaterasu and Issun open the Spirit Gate, he shows up, claiming that Kutone led him there. He sees the Spirit Gate as an opportunity to make the sword glow silver, saying that the monsters of misfortune within will be more than enough satiate the sword. Issun then warns him that there's no telling what may be on the other side of the gate, and that Oki may find more than he bargained for. Oki then says, "That's what I'm hoping for... For the sake of Kutone!" before running through the gate. Amaterasu runs after him, jumping through the gate which closes up behind her.
On the other side, they find that they ended up in Kamiki Village. Oki runs off to fight the monsters, leaving Amaterasu and Issun alone to find out that the Spirit Gate has taken them back one hundred years. The pair then take Nagi to the Moon Cave so he can defeat Orochi. However, Orochi knocks him out, resulting in Amaterasu and Issun going inside the cave alone. She then finds Oki there, who was brought there because he sensed Orochi's dark power. Issun tells Amaterasu that Lika, the Oina girl they were looking for, is on Orochi's back. Shortly afterward, Orochi appears, angered that they have "defiled his sanctuary."
Oki transforms to his wolf form, prepared to fight Orochi. Issun warns him about Lika, to which he responds with "I care not. For Orochi will be my ultimate offering to the sacred sword.". After Amaterasu fights and greatly weakens Orochi, Oki steps in to deal the final blow, praying to Kutone to awaken and glow silver. When he attempts to strike Orochi, the demon's barrier protected him from the attack, and he counters Oki by striking him, sending him against a wall with great force. Oki, confused, asks loudly to Kutone why it will not glow silver while Orochi prepares to kill him.
Before Orochi could do anything, Nagi appears and stops the demon. He joins up with Amaterasu and they both slay the wretched eight-headed demon. Oki, humiliated and angry about what Nagi's sword had done, immediately left the scene, making sure no one saw him. Amaterasu and Issun escape the Moon Cave and go back to their time. They take Lika to Laochi Lake, only to find no one there. They head to Wawku Shrine and find many of Wep'keer's residents there. Tuskle tells them that Oki opened the gate to the shrine, which has caused more of the demon's blizzard to blow through Kamui. Kai also tells them that he was the one to protect Kemu and Samickle, and that, despite doing things that angered the other Oina, he had good intentions.
Amaterasu then explores the Wawku Shrine, and ends up on the Silver Demon's altar. There, before fighting Nechku, she is joined up by her past incarnation, Shiranui. They easily defeat the demon, but before Amaterasu can finish it off, the Gold Demon Lechku crashes in. Oki had found Lechku and was fighting the demon furiously. Lechku throws him off, and joins with Nechku to perform a spell. Oki transforms to his wolf form, intent on slaying the demons himself. Shiranui stops him, but Oki attacks him to get him out of the way. As he jumps in the air to kill the demons, they unleash a spell that freezes time. Stuck in the spell, Amaterasu and the others helplessly watch as Lechku prepares to kill Oki. Luckily, Shiranui was able to break free from the spell, and pushes Oki out of the way, receiving the blow himself.
Shiranui was able to attack the demons but caused him to almost fall off the cliff. Amaterasu catches him in time, and tries to pull him up. Oki, seeing the opportunity to slay the weakened demons, rushes forward but stops when he sees the divine wolves struggling. An ice tree slowly breaks, threatening to crush Shiranui, Amaterasu, and Issun. Before it could harm them, Oki slices it in half. Once Amaterasu brings up Shiranui, Kutone starts to glow silver. Oki finally realizes that the sword would only glow if the wielder's heart was free of selfish desire.
He later tells Amaterasu to find a way to the other altar while he stayed to protect Shiranui. He somehow gets to the other altar before Amaterasu, and joins her to fight the demons. After a long battle, Lechku and Nechku were defeated, freeing Kamui of their evil and the fearsome blizzard. Shiranui, upon seeing Oki's glowing sword, managed to gather enough strength to pass through the Spirit Gate and go back to his time. Everyone then gathered at Laochi Lake, where Lika was performing the Volcanic Incantation. The Ezofuji mountains erupted, bringing warmth to the land.
Oki felt guilty for causing so much grief to his village after taking the Kutone sword. Samickle, the village chief, forgave him by offering his hand for a handshake. Oki accepted, and Wep'keer became a village far too strong to succumb to evil again. Oki then returned Kutone to its pedestal. Suddenly, a flash of light erupted from Kutone, striking the Ark of Yamato. The perpetually frozen ice began to crack, and the iron ark slowly rose in the air.
Despite the harsh cold winter of Kamui, Oki is always seen in his light clothing outfit, which consists of a light short-sleeved shirt of a dark blue shade, a crimson sleeveless vest with white decorations that has a dark blue line on each of the sides of the vest. Oki has dark blue pants with a red belt, which matches in color with the shirt and vest respectively. The Oina warrior has brown footwear that seems to be leather shoes, round guard-like objects on his wrists, and on his waist, the sheath for Kutone is strapped. Oki, like all other members of the Oina, has a mask, his bearing the signature design of what seems like a blue bear with large, horizontal-pointing ears and black eyes with red irises.
Oki has tan skin despite the constant cold climate of Kamui and spiky hair, with the dreadlocks of a shade changing from red to black. He also wears a fang on his neck. In his wolf form, Oki is a muscular male wolf with fur of a primary dark blue color and red on his neck. His mask is now on his forehead, and still keeps his worn fang at its place.
At the first encounter with Oki, he is depicted as selfish, focusing on nothing but slaying more demons and appeasing Kutone's thirst for demonic bloodShiranui's sacrifice to save Oki from a fatal attack, he opened his heart toward others., to the point that he doesn't care for anything, or anyone else. However, after
Oki fights with two forms. In his human form he fights with his sword. Avoiding Oki's attacks while delivering powerful strikes using a Glaive can be advantageous. When Oki summons a group of icicles, Amaterasu should use Power Slash to send them flying back at him. She can then attack him while he is temporarily stunned. Inferno can thaw Amaterasu if she is frozen by any of Oki's attacks. Amaterasu must move close in order to deal damage to Oki but she must be wary of his powerful sword strikes.
After the human form is defeated, Oki will transform into a large wolf and uses ice attacks along with his silver sword. He is also able to create doppelgangers (two at once) which will freeze Amaterasu if they attack or touches her. He gets more aggressive with attacks, though they are easier to see coming and generally easy to jump away from. After a long series of hit and run attacks, Oki will finally give in to Amaterasu.
- He is one of very few characters who Amaterasu cannot attack (after fighting him). He, like Waka, can "phase" through her attacks and will not be affected by any of her brush techniques, unless Amaterasu paints a circle around him with the Celestial Brush, which turns him into his wolf form.
- It is possible to conclude that other Oina can roar while in human form, being that Oki did so before fighting Amaterasu.
- There is a bit of a contradiction between him and Lika. Before fighting True Orochi, he says that he doesn't care that Lika is on Orochi's back, which could mean that he did not care at all about her safety. However, when Amaterasu takes Lika to the entrance of the Wawku Shrine, she tells everyone that Oki told her to "be a good Oina and help everyone". But, later on in the story, it is revealed that Oki's heart was filled with selfish desire, the desire to make Kutone glow no matter the cost. This means that before he did care about Lika, but was willing to risk her safety to make the sword glow.
- Oki is based on the legendary Ainu hero Okikurmi (「オキクㇽミ」?).
- In the Japanese version of the game, Oki follows the pattern of nearly every other member of the Oina tribe in using occasional words from Itak, the language of the Ainu people and also donor of many words, names, and legends that contributed to the stories in Kamui
- Oki appears as a silhouette in the opening sequence of Ōkamiden.