From 2009, Kazumasa worked for seven months in Uganda as a member of the Japan Overseas Cooperation Volunteers (JOCV) and later became a non-profit organization.

He has been working with JICA, WHO, and the Ugandan Ministry of Health to promote the use of alcohol hand sanitizers in medical facilities to prevent nosocomial infections through hand hygiene. In 2016, he moved to the Nairobi Branch of Mitsui & Co., Ltd. and has been engaged in investment projects and logistics business in Eastern Africa as a new business development officer. In the last couple of years, he has been focusing on start-ups, agriculture, manufacturing and healthcare investments in Ethiopia and Kenya, as well as developing internal business strategies for Africa.