Chika Idol wo Kage de Sasaeru Ore
A relationship between Natsukawa, a flashy gal-type classmate, and Kageyama, a plain and unassuming boy. Despite appearing to have no connection, Kageyama secretly receives a message from Natsukawa: βMeet me at our usual karaoke spot after school.β He joins her for a private karaoke session, where he reveals something she had asked him to prepare.
(Source: Natalie, translated)