The following mainly comes from initial traditional tribes in general, not including tribes who have mixed origins and other case-by-case variable exceptions.
As one of the nine foundational tribes, the [Oni Demon Tribe] were initially as mountain-living tribes who have deep tradition of warrior-associated customs such as holding certain symbolic rituals that was associated with war and warrior's death. After receiving their own Grimm-form,
[Grimm-form appearance]
black (Japanese Oni-face-looking) demon tattoo on face
black muscular curved branched tattoos covering on full body's external outline (such as the side of the limbs)
dark-purple skin
two small slightly upper-toward curved horns on forehead
[Grimm-form ability]
enhanced physical condition (enhanced strength, enhanced speed, enhance endurance)
regenerative healing factor (able to heal up considerable number of penetrating wounds)
Combat Application:
[Societal Aspects]
[Cultural Aspects] In terms of residence,
In terms of tribal settlement,
In terms of food source,
In terms of beverage,
In terms of recreation,
In terms of trading activity,
In terms of clothing,
In terms of toolmaking materials,
In terms of their usual go-to weaponry,
In terms of religion,
In terms of festivals,
In terms of mythological fictional creatures within their oral tribal folklores,