Oni as Bogdashkan Jungle Orcs
by Marc SaindonWest of Yasuko, the tribes of Bogdashkan Orcs are susceptible to more mutations (a trait also found in the "Bakemono" Goblins I've suggested), creating a wider range of coloration (blue, red, black, yellow, etc.), and the presence of horns.
They don't get along well with the Rakastas (as the Oni appreciate tiger pelts as clothing), but also war a lot among themselves. Once in a couple of generation, a tribal leader leader unites the Oni into one great horde, and they go on a "village pillage" spree; because Yasuko has the nicer stuff, it's the usual target.
Individual Oni (especially PCs) might be more civilized, or at least have enough knowledge of Yasukan culture (e.g.: avoid wearing tiger skins) to at least find work as mercenaries (even against their own kind, coin is coin), bouncers and leg-breakers in Yasuko, although they will always start in the lower castes. Oni can be Barbarians, Fighters or Rogues, although a handful of "Enlightened" Bodgashkan Orcs have had successful careers as Monks. The Clerics and Magic-Users will go for the darker stuff.
Orcs as Oni don't match exactly the mythology, although you could assume that due to limited contact between Bogashkans and Yasukans aside from war, differences that pop up might just be folk tales people of Yasuko tell their children so they'll behave.
Notes:
Oni
(Image from: https://www.deviantart.com/cyclone62/art/Oni-836694195)