Hello, I am one of the developers of this game. Thank you very much for your interest in and playing our demo game. Currently, there is a bug where the master volume disappears when moving to the next stage. This can be resolved by going to settings -> audio and lowering the master volume from 100 to 0, then raising it back up. We apologize for the inconvenience caused by this bug, and we will strive to release an improved game driven by your interest. Thank you!