He also researched the moribund Ainu language in northern Japan, and worked on Inner Asian languages and Kra–Dai languages, especially those preserved only in Chinese transcription, as well as on Old and Middle Korean texts.
In his research, he examined the nearly extinct Ainu language spoken in northern Japan, and concentrated on languages from Inner Asia and the Kra–Dai family, particularly those documented through Chinese writing systems, and also studied ancient Korean texts.