When the Earth faces a threat from alien beings called the Oni, they propose a bizarre challenge—a human must defeat Lum, the enchanting daughter of the Oni leader, in a game of tag to prevent the invasion. Unluckily, the chosen competitor is the amorous high schooler Ataru Moroboshi. With just 10 days to catch Lum by her horns, Ataru realizes the near-impossibility of the task against her unearthly abilities. Driven by the promise of marriage from his childhood friend Shinobu Miyake, Ataru seizes a moment of vulnerability to grab Lum, albeit mishandling her bikini top before achieving his goal. Despite the game's end, Lum misinterprets Ataru's intentions and moves in with him, sparking a comedic struggle as Ataru navigates Lum's affections while seeking reconciliation with his true love. As Ataru's unintended triumph leads to chaotic consequences, his future luck remains uncertain.