Idol Debut is the thirty-first episode of Engine Sentai Go-Onger.
The Go-ongers face a mysterious monster who starts feeding on sound waves upon emerging from another dimension. When the Go-on teams attempt to fight the monster, they only end up enlarging it before it falls asleep. To further confuse things, the Pollution Ministers suddenly arrive to play the song "Gaiark Industrial Revolution Declaration."
The ministers explain that the monster, whose name is Lumbiaco, is from the Sound World. Lumbiaco feeds on high-pitched sounds to increase its size and only a "beautiful song" can keep it from growing so big that it literally crushes the planet. Unfortunately, the Gaiark's music only served to increase Lumbiaco's size. Hiroto sings a ballad to try to shrink Lumbiaco, and his song initially seems to work, but the monster awakens in a rage afterwards and grows further. When it is determined that only a female voice is able to shrink Lumbiaco, Kitaneidas and Yogostein make matters worse when they dress up as drag queens and try to sing again, and Lumbiaco grows even larger.
Hant and Gunpei assemble GunBir-Oh, who fails to put down the ever-enlarging Lumbiaco. Meanwhile, Saki suggests to Miu and Kegalesia that they should form a 3-girl idol group. Though the three initially clash on how to properly train to become an idol group, Saki, Miu, and Kegalesia eventually come together and, calling themselves G3 Princess, return to the scene and sing "G3 Princess Lap ~PRETTY LOVE☆Limited~" and shrink Lumbiaco back to normal size. After Go-on Yellow, Go-on Silver, and Kegalesia finish the monster off, Saki and Miu are pleased with the newly-formed collaboration, but Kegalesia rejoins Yogostein and Kitaneidas, much to her now-former groupmates' bitter disappointment.