The Melody of the Heart (Otoya x OC x Reiji)

With eyes that are a bit too sharp and skin that is a bit too cold, people fear Akimoto Yui, despite her lack of ill-intention. To avoid the stresses of social interaction, she conceals herself behind the thin shield of her glasses.
But her long-time friend, Kotobuki Reiji, is instructed to find new ways to teach his underclassmen, and thus, he and Ittoki Otoya register for a camp during their break in their idol careers. Kotobuki also manages to convince Akimoto of her talents, causing her to take a leap of faith and sign up for the course as well.
Promising to assist her musicianship among the trials faced at the camp, Kotobuki and Ittoki invest their idol talents in Akimoto, but what they develop is more than taboo in the music industry...
Each young man begins to strive for the heart of the young composer, developing a rivalry that may tear them up as a unit.

(I only own Yui Akimoto and the story-line. Uta no Prince-sama and the characters belong to their rightful owners.)