Wave Music 5
Wave Music 5 is the background music for the following waves: E1M5, E1M9, E2M5, E2M9, E3M5, and E3M9. It has yet to be determined if this layout of every fifth and ninth episode was intentional or accidental. Since it plays on every ninth wave, it is the most used background music, and it's also the music for each episode's boss. The song uses a distorted electric guitar for its melody.