Under Desert Sands, Part 1 - S1.E27

The Rave crew began heading East to look for the rave of combat, but along the way they fell into a crack and ended up at a city beneath the surface that somehow still has a sky. They were accussed of being monsters until they realized Haru was the Rave Master, so they then asked for Haru's help to stop the monsters attacking their city. Haru was about to accept until he found out that the enemy was led by his father. Meanwhile Musica found out the leaders of the city were just pretending to know where the Rave stone was, and Haru began attacking the mosters trying to draw out his father.