As a child, Mutō joined FC Tokyo’s youth system, where he kept developing until 2010. He then enrolled in the Faculty of Economics of Keio University but kept playing football, for Keio’s team. Despite an injury which sidelined him, in his first season with Keio he won the “Rookie of the Year” title. In 2012 and 2013, FC Tokyo included him in their roster as a “Special Designated Player”, an option that allows JLeague clubs to field university players without a professional contract. However, he got on the pitch just once, at the end of a match in July 2013.