When extraterrestrials called the Oni threaten to overrun Earth, they vow to depart if a single human can beat Lum, the stunning daughter of their chief, in a solitary game of tag. The chosen "lucky" individual turns out to be the indulgent and hapless high‑schooler Ataru Moroboshi. With ten days to seize Lum"s horns, Ataru quickly sees the task is nearly impossible because of her alien abilities.
Encouraged by a marriage promise from his childhood friend Shinobu Miyake, Ataru manages to catch Lum off guard. He initially grabs her bikini top by mistake, yet ultimately secures his real objective. Although the contest ends, Lum mistakenly believes she is the one Ataru intends to marry and opts to move in with him. The beleaguered student constantly attempts to shake off the clingy Lum while trying to reconcile with his intended bride. After Ataru"s daring triumph ends in such a catastrophic result, it is doubtful whether fortune will ever favor him again.
Despite his confidence, he realizes destiny may still conspire against him and face unforeseen trials soon today.
