Kōji Seto (瀬戸 康史, Seto Kōji, born May 18, 1988) is a Japanese actor and singer. His major works include lead roles as Wataru Kurenai in Kamen Rider Kiva and Hiro in Koizora; and supporting roles as Satoru Okura in Atashinchi no Danshi, Ariake Yamato in Otomen, and Eiji Kikumaru in Tenimyu. He stars as Mori Ranmaru in the drama, Gō: Hime-tachi no Sengoku.
In 2010, he was named one of the most promising actors and actresses, placing 7th in a poll conducted by Oricon. Through his role with Kamen Rider Kiva, he was also the lead vocalist of the J-Rock band Tetra-Fang. The lively and bright multi-talented Seto is nicknamed Setomaru (瀬戸丸) and is a member of the acting group D-Boys.
Born in 1988 in Kyushu, Kōji Seto grew up as the oldest child with two younger sisters. His childhood dream of becoming a vet changed suddenly with the end of his Junior High School time, when he watched with 15 years the TV series Orange Days. The praised drama and performance by Satoshi Tsumabuki inspired his wish to become an actor. After discussing his plans with his parents, they decided to support their son and enrolled him to a local acting school.