Masakatsu Morita (森田 必勝, Morita Masakatsu, 25 July 1945 – 25 November 1970) was a Japanese political activist who committed seppuku with Yukio Mishima in Tokyo. Morita was the youngest child of the headmaster of an elementary school. Losing both parents at the age of three, Morita was cared for by his brother Osamu and educated at a Catholic school. He entered Waseda University in 1966, but was dismayed by the presence of Communists Zengakuren students at the University and became heavily involved in the small right-wing faction at the university. He first met Mishima on 19 June 1967, and joined the Tatenokai at its establishment in October 1968. As early as March of that year, he had written a letter to Mishima expressing a willingness to die for him.