Immerse yourself into a fascinating side story to Kyoukai Senjou no Horizon. It originally came in a bundle with the first press release of the odd-number Blu-ray volumes of the 1st and 2nd seasons of the anime.
The side story you’re about to get familiar with takes place a year before the main events. While on the board of Musashi, Kimi, Mitotsudaira, and Asama decide to create their own music band. Asama is the initiator of this endeavor. The newly-created band is going to participate in the upcoming music festival in Aki, which is currently governed by K.P.A. Italia.