Koichi Oita played both halfback and fullback positions. While attending Tokyo Imperial University he represented Japan in the Berlin Olympics of 1936. Oita played defensive halfback breaking Sweden in the “miracle of Berlin,” in which Japan came back to win in the second half from two goals down against Sweden. In April 1938 came his last appearance for Japan against Islington Corinthians. After his active career, Oita joined Sumitomo Metal Industries and became manager of the company’s football team (now Kashima Antlers) from 1947-56. For Sumitomo, he held various higher management positions. Later, he also served as Chairman of the Board of the companies Sumikin Bussan and Daikin Industries. At the age of 82, he died of heart failure.