Koko ga Genkai no Oval Gakuen

is a japanese manga series written by Ooi Masakazu and illustrated by Maki. It began serialisation in the September 2013 issue of Manga Time Kirara Forward.

The series was released under 3 volumes from February 2014 to June 2015.

Synopsis
In the near future world where there are only women, the girls of Oval Academy will use "music" as a weapon to fight against the mysterious and mighty foreign enemy "Hishibutsu". Volume 1 to enjoy the destructive power of "Bishojo x SF"!

(Source: Amazon JP - Translated)