Koseki Yuta, alternatively written as 'Koseki Yuuta', is a Japanese actor. He's been active in the entertainment business since 2003 and has starred in commercials for products such as "Phantasy Star Portable 2" and plays such as "Musical Shugo Chara!". He is mainly known for his part in the "Prince of Tennis Musicals" (Second Generation) as he played Kikumaru Eiji. He also appeared in the Shugo Chara Musical, in La Corda de Oro Musical and played the main character in the rerun of the Amuse stage play, FROGS.

He appeared in some movies and dramas such as "Ooku", "Bitter Blood", and "Oyaji no Senaka"