Koji Seto (瀬戸 康史 ,Seto Kōji?, May 18, 1988(1988-05-18)) is a Japanese actor, entertainer and singer. He previously starred as the shy young hero Wataru Kurenai in Kamen Rider Kiva. Koji is also the vocalist of the J-Rock Band TETRA-FANG. The lively and bright multitalent is nicknamed Setomaru (瀬戸丸) for playing Eiji Kikumaru in the Prince of Tennis musical series, Tenimyu, and is one of the youngest members from the acting group D-BOYS.

Source: Wikipedia