The Ainu are an ethnic group comprising related Indigenous peoples who are native to northern Japan, including Hokkaido and Northeast Honshu, as well as the land surrounding the Sea of Okhotsk, such as Sakhalin, the Kuril Islands, the Kamchatka Peninsula, and the Khabarovsk Krai; they have occupied these areas known to them as "Ainu Mosir", since before the arrival of the modern Japanese and Russians. These regions are often referred to as Ezochi (蝦夷地) and its inhabitants as Emishi (蝦夷) in historical Japanese texts.

Hokkaido is the second-largest island of Japan and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel.