Scholar of Japanese language studies. Influenced by his father Otsuki Bankei, a Confucian scholar, he studied Chinese studies since an early age. Interested in Western studies, he learned English studies and mathematics at the Kaisei-jo school and Daigaku Nanko. In 1872, he started serving at the Ministry of Education. Starting in 1875, he compiled the first modern Japanese dictionary in Japan, Genkai (1889-91). He also wrote the books Ko-Nihon-Bunten, Kogo-ho and Kogo-ho Bekki, and made great contributions to the study of Japanese grammar. In his later years, he worked on compiling a Japanese dictionary, Dai-Genkai, which was a revised and enlarged version of Genkai. After his death, Dai-Genkai was published in 1914.