Ataru Moroboshi, a second-year student in Class 4 of Tomobiki High, is arguably the most perverted boy in history. Despite having his childhood friend Shinobu, he constantly hits on girls everywhere, even willing to risk his life for a beautiful woman. One day, an alien oni tribe invades Earth, and their leader demands that each side send a representative to decide Earth's fate through a race. The perpetually unlucky Ataru unsurprisingly becomes the "chosen one," while the oni tribe sends the leader's daughter—a petite beauty in a bikini, with upturned eyes, who can fly and shoot electricity—Lum. This crucial race ultimately ends with Ataru's victory, but Lum falls in love with this unreliable opponent. From then on, their destinies become tightly intertwined, leading to a series of magical, hilarious, and touching stories...