However, Mishima's talents lay in sports, and he was active in college baseball, judo, horseback riding, boating, sumo, and skating, participating in numerous competitions.

Although a number of qualifying events had taken place, support for the Olympics was not forthcoming from the Japanese Ministry of Education, and the budget was limited to sending only two athletes to Stockholm.

Mishima and long-distance runner Shizo Kanakuri were the two selected and travelled to Stockholm over the Trans-Siberian Railway.

He left Stockholm before the closing ceremonies to visit Berlin, where he examined the grounds for the 1916 Summer Olympics, and to purchase sports equipment then not available in Japan, returning home only on February 7, 1913.

In 1913, Mishima joined the Yokohama Specie Bank and was assigned to its branch office in Tsingtao, China, where he remained until 1939.