A Western-style painter who studied with Okada Saburosuke (1869-1939). Immediately after graduating from the Tokyo School of Fine Arts in 1909, the year before Japan formally annexed Korea, he took up teaching duties in colonial Korea, one of a number of Japanese artists who taught there. He served at the Kyongsong (Gyeongseong) Middle School (a school for Japanese students that later became the Seoul Middle and High School) beginning in 1909 and stayed in Korea until 1945. In 1941 he participated in the founding of the pro-Japanese Kyungsung Artists' Association 京城美術家協會 (경성미술가협회), "the first large-scale organization organized for artists' pro-Japanese activities."² His brief memoir of his life in Korea provides information on the Japanese artists who went to Korea and what they did during the colonial period.³

In the early 1950s he began designing woodblock prints for the publisher Kyoto Hangain. Most of these works consist of scenes of Korean customs and scenic places, idyllic remembrances of Mamoru's many years living there. Typically, they are signed M. Hiyoshi with a stylized seal of Mamoru [守], as shown below.