The girls' band Mayonnais, formed by high school freshmen in the rural countryside, has never once drawn a single audience member to their live performances. Desperate for anyone at all to hear them play, they make a prayer to the gods—and their wish is answered in completely unexpected fashion. The live house they practice in suddenly connects to a dungeon in another world. Adventurers, goblins, dwarves, and other non-human inhabitants of that fantasy realm begin to pour through the portal, becoming the band's first real listeners. What follows is an unprecedented fantasy music comedy as the three high school girls—guitarist Mayo Wajima, bassist Tama Suzuki, and drummer Shio Nakajima—navigate both their real-world high school lives and their growing reputation as a live act for an otherworldly audience. A young magic user named Talica soon joins the band, expanding their sound and deepening the connection between worlds. Not everyone in the other realm welcomes the music. Queen Tina, a ruler who disapproves of the band's activities, joins the live house manager's own band and challenges Mayonnais to a head-to-head live battle. Through stage performances, comedic cultural clashes between modern music and medieval fantasy society, and a growing roster of fans on both sides of the dungeon door, the story explores themes of connection, self-expression, and the universal appeal of rock music. The narrative draws heavily from real-world musical culture, with chapter titles taken from famous songs by artists such as Metallica, Kishidan, Sakanaction, and BUMP OF CHICKEN, and the characters themselves named in homage to the Japanese heavy rock band Ningen Isu.