Ryu Mitsuse (光瀬龍 Mitsuse Ryū?, March 18, 1928 – July 7, 1999) was a Japanese science fiction writer. In the West he might be best known for manga-related works and the story The Sunset, 2217 A.D. which appeared in Frederik Pohl's Best Science Fiction for 1972.
Mitsuse was born at Minami-Senju, Kita-Toshima District, Tokyo Prefecture in 1928. His birth name was Chiba Kimio (千葉 喜美雄?). After marriage he adopted his wife's surname as his surname, taking the name Iizuka Kimio (飯塚 喜美雄?).
He went to Tokyo in 1948. He entered into various schools, that is, the Toyo University and the Meiji University. But he stayed there for several months. He entered into Kawamura High school in 1948, and graduated from this school. He entered into the Department of agriculture in the Tokyo University of Education in 1949. He graduated from the Department of science of this university in 1953.
Mitsuse joined Kagaku Sousaku Club where Takumi Shibano was operating as a publisher and an editor of the Fanzine Uchuu-jin. He started publishing various short novels in the fanzine Uchuu-jin (宇宙塵?) under the pen-name Mitsuse Ryu.