If you're looking for manga similar to Koko ga Genkai no Oval Gakuen, you might like these titles.
Miya made a bold high school debut in an attempt to change from her once *infamously* boring self. She gets involved with another girl named Hiyo, and is convinced to enter the beautiful world of Japanese traditional instruments. Inspired by a mesmerizing live performance, Miya ends up joining Hiyo's quest to establish a "Japanese music club" and form a Japanese instrument ensemble.
Ririsa Suzunomiya, who is forced to live a cramped life at a girl's school where genuine ladies gather, is drawn to the sounds coming from the old school building...? The gorgeous and ladylike girls shout with beautiful sparks!
Takurou Hibinuma, a third-year in high school. He is a boy who gets bullied, and has no talent in studying or sports, but the only thing he can call his own is "rock." He experiences many things through music, and aims to become a rock star
Hosaka Mao's never stood out. Her father's a washed-up rock-and-roller. Her hair reminds people of Pippi Longstocking. She's nowhere near the in-crowd. The arrival of long-haired beauty Hasekura Yokiko changes everything...
Although his father is a composer, and his mother a concert pianist, WAKANA held no love for classical music. Instead, the music he likes accompanies characters and stories. He was a fan of soundtrack music, especially soundtracks for anime and games. But he had never dreamed of composing his own pieces... until one day he met his classmate, who was also a comic writer. It was then that the dream finally began to hatch.