Mon

Yes. At the time it was a land of Ainu, before Japanese invasion and colonization as well as cultural extermination. Ainu are culturally and, genetically very distinct people than “Yamato/Wajin” people that make Japanese population. The language is also separate e.g. Nupuri vs Yama/zan for mountain. Shumari vs Kitsune for fox. They also have distinct beliefs, traditions, wear. One Ainu story is that the world started with Yotei, or that the mountain is a husband of Shiribetsu pending on a tribe.

The castle visible in the trailer is most likely Matsumae castle, the starting point of invasion, Date could be another contender for “Japanese stronghold”.

Think Native American vs British essentially.

Ainu could have some relation to Emishi people of Akita that also suffered from Yamato.