Among his many works of scholarship, Tsuboi proposed and advocated for the theory that the first indigenous people to occupy the Japanese islands were a people who appear in Ainu legends as the ''[[korpokkur]]''. His so-called "korpokkur theory" was hotly debated by others of the time. | Among his many works of scholarship, Tsuboi proposed and advocated for the theory that the first indigenous people to occupy the Japanese islands were a people who appear in Ainu legends as the ''[[korpokkur]]''. His so-called "korpokkur theory" was hotly debated by others of the time. |