OK, the food here isn't dramatically different from what a Japanese diner would serve, but you can get a donburi (rice bowl) topped with Hokkaidō venison and gyōja niniku (alpine leek), the local aromatic that has a long history in Ainu cooking. Also available is pochie (ポッチェ; ¥700), fermented potato dumplings. The decor is an eclectic mix of Ainu items, drum sets, microphones, and so on.
Ask one of the staff to put on a video of owner Atuy and his group performing traditional music and dance.
There's another branch in the Ainu kotan in Akanko Onsen.