TV-Series
Description
Kōji Mihama is a human male around 15-16 years old, born January 14 under the Capricorn zodiac sign. He possesses ash brown hair, often tied in a ponytail in later years, and chartreuse or olive green eyes. He wears his deceased father Takeyuki Mihama's dog tag and a matching purple bracelet symbolizing his unit, Over The Rainbow.

His early life involved learning cooking and guitar from his father, fostering a cheerful personality. After Takeyuki's death in a car accident, he became quiet and withdrawn. He attended Edel Rose academy, where classmates mocked his "childish" music until befriending Hiro Hayami. At 15, he formed the unit Hiro x Kōji with Hiro and composed their debut song "Pride." Hiro claimed sole credit for the song under supervisor Jin Norizuki's advice, causing Kōji to quit Edel Rose in anger and betrayal.

Depressed and musically stifled, he frequently played guitar on a rooftop. Naru Ayase heard him and later requested one of his songs for her Prism Show. He initially refused but relented after recognizing her sincerity, composing "Heart Iro Tori Dream" for her. This encounter restored his passion for music.

He developed a relationship with fellow musician Ito Suzuno. When Hiro commissioned Ito for a song, Kōji intervened, fearing Hiro would steal her work. He gave "Pride" to Hiro to prevent this, later explaining to Ito that the song was a love letter to her. They began dating but faced familial opposition; Ito's father caused the car accident that killed Takeyuki. The families forbade their relationship, leading Ito to break up with Kōji temporarily. After confronting their families and resolving the feud, they reunited.

He reconciled with Hiro after Hiro apologized for stealing "Pride." With Kazuki Nishina, they formed Over The Rainbow. Kōji composed their songs, including "Freedom," whose lyrics conveyed forgiveness to Hiro by referencing their shared past.

In later years, his personality returned to its original liveliness. He expanded his career beyond Over The Rainbow, hosting a TV cooking show and composing internationally, including a Hollywood film soundtrack to help repay Edel Rose's debts. He joined the band Cross Road with Ito and her brother Yuu. He remained Over The Rainbow's costume designer and youngest member.

Trivia includes his kanji name variations (e.g., 浩司 meaning "prosperous officer") and surname Mihama (神浜, "god beach"). He is left-handed and uses his father's guitar. His song "Sweet time Cooking magic" originated from childhood kitchen sessions with Takeyuki.