This collection could be obtained by redeeming the serial code included in the August 22nd, 2019 issue of Weekly Famitsu through GUST's website.
Included is a short version of the game's opening theme and 3 medleys of an assortment of tracks from the game's soundtrack.
All files are 128kbps MP3s and include no embedded art, composer or artist information. The following credits were taken from KECH-8081~2


1. Extra Mixing Music -　Battle Theme
  1.1 End of Hibernation
    Composed & Arranged by Hayato Asano
    Bass: Makoto Kawaraguchi
    Mixing Engineer: Takashi Saeki

  1.2 Southern White Wind
    Composed & Arranged by Hayato Asano
    Guitar: Kenji Kakuta
    Bass: Ryuichi Hagi
    Violin: Kei Ono
    Mixing Engineer: Takashi Saeki


2. Extra Mixing Music -　Character Theme
???

3. Extra Mixing Music -　Event Theme
???

4. "Rainbow Summer" Game ver
  Vocal & Chorus: Sayaka Kanda
  Strings: Kashiwagi Strings
  Guitar: 柳生俊彦
  Bass: Yosuke Kinoshita
  Lyrics: Mari Yoshida / Kosuke Mizukami
  Composed & Arranged by Kosuke Mizukami
  Recording Studio: Sound City / ODEN STUDIO
  Recording Engineer: Chinatsu Koizumi
  Record Assistant Engineer: Haruki Saito
  Mixing Engineer: Kosuke Mizukami
  Artist Coordinates: Toshio Chigira