The Oina tribe are the native tribe of the Kamui region of Nippon, known for their unique ability to shape-shift. Being that they are disconnected from mainland Nippon, their culture and beliefs have developed outside of the dominant culture of Nippon, much like the Ainu people they are based on.
The Oina are a race of shape-shifters, with the ability to change between a wolf and human form at will, or by drawing a circle around them. Most bear dark, wavy hair, with very few exceptions. Their main distinctions, however, come from their unique aesthetic. Members of this tribe wear masks bearing animal faces that reflect their inner personalities. For example, the calm, collected, and calculating Samickle wear the face of a peregrine falcon, a bird recognized for its strength and precision the world over. These masks shift alongside their wearer to become head adornments in wolf form.
The general attire seems to be more colorful versions of traditional Ainu clothing, with the patterns bearing a particularly heavy resemblance. Various ethnic adornments and necklaces bear a strong yet stylized resemblance to tamasay and shitoki. These accessories remain around the wearer's neck or on their head, while the coloration of their hair and general attire becomes the basis for their fur color and markings when in their lupine forms. Their general bodily structures also affect their shapeshifting. Females of slender forms have these traits reflected in their wolf forms; small children are represented as young wolf cubs; males are given a more sturdy, strong appearance; and merchants, following the general rule of the world, obtain a more plump form, similar to their human ones.
The Oina are, by nature, not terribly adventurous people. Despite having obvious means of being able to do so, they have never left their icy home in search for warmer lands. The same cannot be said, however, of the Ainu, leading to the conclusion that there may be some similarities between the reality of the Ainu's forced emigration and the lack of travel found within the Oina tribe.
For reasons that are never quite explained, all members of the Oina tribe, young and old, don a mask which hides their face, concealing their true appearance from Amaterasu for the duration of the story. However, one can see unused masks hanging in Kemu's house, so it can be assumed that this is some kind of tribal rite of passage or ritual. In addition to this mysterious piece of their culture, the Oina also practice a polytheistic animistic religion, much like Shintōism. A central deity is never defined, but it can be assumed from conversations with members of the tribe that they believe in and worship all of the things and value them equally. However, until the events towards the end of the story, it is unknown as to whether or not other members besides Kemu and Tuskle can initially see Amaterasu's true form, as she is not a divine being they would have heard of, nor have had much experience with, as most of her journey in her previous life as Shiranui took place in mainland Nippon.
The tribe itself is rather loosely organized but has four distinct classes: Elder, Warrior, Commoner, and Merchant. The Elder of a tribe serves as an all-powerful but reasonable leader over the rest of the people. Leadership is presumably passed on when the current Elder decides it is time, but the procedure for deciding the next Elder should the current one die remains unknown. The Warrior class is a smaller one, consisting entirely of strong men in the tribe, who patrol the entirety of Kamui in search of outsiders, and acting as the first line of defense and warning in the case of invasion by another race or demons. The Commoner class—or general middle class—consists of the bulk of the members of the Oina tribe. They make up the basic workforce, contributing necessary labor to produce the supplies needed to survive. The only outlying class that does not seem to have too much relation to the main groupings is the Merchant class. Merchants, who by definition are destined to travel to sell their wares, are relatively isolated from the main tribe. It's reasonable to assume that the Oina, being a rather insular community, would shun those who voluntarily choose to leave the tribe and travel the world, yet the true reasons for this remain unknown and a trait shared by other Merchants found in other parts of Nippon.
As most of the landscape this tribe inhabits is almost always covered in a thick layer of snow and ice, there are not many readily available resources other than fish, hunted prey, and lumber, evidence for all of which can be found in or around the homes of the Oina. Dried meats can be preserved and stored for later consumption, making the season where prey is less common more bearable. In cases where there is a surplus, it's possible that the merchants in the area take to the road and sell their wares to the people of Nippon. The use of wood is also common in the construction of homes, shrines, protective walls, and other structures seen all over. Well-packed snow is also used in the construction of the exterior of homes, creating a one-room building, often sporting a chimney for the release of smoke from the fires that are kept lit inside for warmth. Larger homes occasionally have a secondary room on the floor above, yet it is inaccessible to Amaterasu during her journey. These secondary rooms may provide extra storage or serve as a bedroom of sorts, which would separate the common room from the living area. However, the true nature of these room remains unknown.
Because the Oina maintain distance from others, both in the figurative and literal sense, it is difficult to determine their exact relation with the various races dwelling in Nippon. However, non-Oina humans do inhabit Kamui, and while it remains unknown as to how much or little trust is awarded to them, acceptance into their tribe does appear possible. Agata Forest's Kokari sports the standard attire of the tribe, and has even been gifted a rabbit mask, though he wear it on his head instead of his face. He is also permitted to fish on one of the few unfrozen sources of water in the entirey of Kamui. However, his proximity to Onigiri-Sensei's dōjō is notable because it would appear that the tribe keeps outsiders not only distant from the main village, but also under the watch of one of their warriors, since Oki's house is not too far from either of them.
While the miniature humanoid race of the Poncles live in the neighboring forest of Yoshpet, very few members of the tribe have ever met one other than Issun, who was mentioned to have made frequent visits to the village of Wep'keer accompanied by Kai. Little information can be obtained to fully describe the interactions between these two races, but it would appear that no ill will or hatred is harbored by or towards the other race and that they would like interact more if not for the civilizations being separated by the dangerous forest of Yoshpet.
When the Ark of Yamato fell from the Celestial Plain, the ancient Oina witnessed its descent and noted its landing in the Lake Laochi, where it would rest for several centuries. The boat gave rise to many demons that scattered across Nippon, and eventually the twin demons Lechku & Nechku. However, these two only appeared after True Orochi's defeat and remained as altar statues so long as someone was there for perform the Volcanic incantation, a sacred ritual to provide warmth during the cold winter ahead from the twin volcanoes the demons called home.
While the exact details of the Ark's descent have been lost to time, the Volcanic Incantation has stood the test of time and is still performed to bring about the eruption of the twin peaks belonging to Ezofuji. However, after Orochi's defeat and the emergence of a black cloud of demonic aura, the twin demons Lechku & Nechku of old are revived and wreck havoc on the land through the use of a machine that will create an endless blizzard. They lure Lika through the Spirit Gate and attack Kemu, leaving no one with the power to perform the Volcanic Incantation. Without this special ritual, the land will freeze over, and its inhabitants will rapidly cease to be.
Upon arrival, Amaterasu and Issun are assaulted by the chilling winds and icy cold of the blizzard that has engulfed Kamui. Issun makes a request that the two find somewhere to get warm before they freeze, and unknowingly take shelter in the home of Oki, an Oina warrior. Oki non-verbally challenges Amaterasu to a fight, seemingly because he is enraged that an outsider has trespassed and entered his home. After Oki's defeat, Issun demands answers for why Oki had taken possession of a sacred sword and then challegned Amaterasu. Oki then recognizes Issun before explaining the current situation. After the reawakening of the Twin Demons, disappearance of Lika, injury of Kemu and subsequent naming of Samickle as chief elder, Oki took it upon himself to take the treasured sword Kutone and slay as many demons as he could until the blade shone blue, as stated in the prophecy. Afterwards, he tells the heroes to return to where they had come, before taking off to continue his mission.
The Oina are based on and share many similarities to the Ainu people of Northern Japan. Many names for characters, locations, and races are borrowed from Ainu culture and transformed in the ones known in the games. The words "oina" and "wep'keer" refer to the shorter epic poems chanted by women, and the word used in general to describe fairytales, folklore, or mukashi-banashi. The naming of Kamui comes directly from the word "kamuy", which loosely translates to "god" or "spirit", and shares its roots with the Japanese concept of Kami.
The land of Kamui itself is the real life Hokkaido, formerly known to the Ainu as "Ezo", which is where Ezofuji obtains its name. As a result, characters from this region use a mixture of Hokkaidō-ben and Itak when speaking to Amaterasu and Issun. The Oina also share many of the traditional styles of clothing and patterns often seen and associated with the Ainu, with the exception being the use of a mask to hide one's face. Because Ainu women have tattoos applied around their lips, resulting in a black crescent moon shape around the mouth, it is possible that the inclusion of a mask was to conceal this fact and allow for a positive reception of a fictionalized Ainu race by the Japanese people.
While most of the characters and races in Nippon have ties to Japanese mythology, the members of the Oina tribe and the Poncle race all have roots deep within Ainu mythology, and these representations are not forgotten here either. Oki takes both his name and general appearance from the demigod Okikurmi, the embodiment of the life and hope in the land of the Ainu. Okikurmi is also believed to have been the father to the first Ainu, following his marriage to Kaipoku, who is represented in the Oina tribe as Kai. Kemu is reborn into the world of Kamui from the mountain god, Kemushiri, from whom he also takes his name. Kemushiri is notable for rescuing the sun goddess of Ainu mythology, Chup Kamuy when she was abducted by a demon. Tuskle too pulls her name from Ainu mythology. The Tuskle appearing in old myths was a shamaness with an affinity for divinity and was a well-known medium. Now, little Lika may not be a famous goddess, but her name still holds a great deal of significance. In Itak, Lika's full name, Pirika, is an adjective that means "beautiful", "sacred", or "big". When coupled with the symbolism in her butterbur leaf mask—the root of which is commonly used to calm fevers, asthma, and colds—one can see the reason behind her being able to protect the icy land of Kamui.