"Megachu!" follows Kousuke, a regular college student haunted by recurring nightmares in which he becomes a rampaging sex demon. His life takes a wild turn when three goddess sisters appear—not to grant wishes, but to stop the evil seed lurking within him that could bring about the world's destruction. To combat this, the goddesses move in with Kousuke, using unconventional and erotic means to fight the demon inside him, blending comedy, action, and supernatural romance.