The original sound track of Warawara Invaders. The file format is ogg. then you can play with the ogg format compatible player. For most musics, recommended to play with "loop playback" function.
How to access DLC contents
Steam Client > LIBRARY > GAMES > Warawara Invaders > Click right button to Open Prorerties > Choose "LOCAL FILES" tab > Press "BROWSE LOCAL FILES" button > When the Explorer opens, open the ost folder of the displayed directory > You can see contents files.