At age six, he was adopted into his maternal line by Iwamoto Hanji (巌本 範治).

In cooperation with Kondō Kenzō, Iwamoto started a magazine Jogaku shinshi (女学新誌) which existed only one year in 1884.

He called for better education for women, the expansion of their civil rights, and for the refoundation of marriage on the basis of love and respect between husband and wife.

Still, he held that women's place was in the home—they would be educated to run efficient, hygienic, and economical homes so as to raise intelligent, moral, and service-minded children.

Beginning in 1885 Iwamoto helped to found and taught at Meiji Girls' School (明治女学校, Meiji Jogakkō) in Kōjimachi, Tokyo with Tsuda Umeko, Kimura Kenzō, Shimada Saburō, and Tada Umachi.