When Ataru lays eyes on the curvaceous Lum, he readily agrees to take on the task of touching the tips of her tiny horns. Alas, when the contest begins, he finds out that the Oni forgot to mention one small matter - Lum can fly! When all seems lost, his girlfriend Shinobu promises to marry him if he wins. Inspired to new lows of deviousness by the prospect of getting just to first base, Ataru pulls it off.
Unfortunately, Lum misinterprets his victory cry as a proposal of marriage to HER, and promptly agrees.
So Ataru ends up with Lum living in his closet, planning their wedding, and zapping him with high-voltage shocks if he even looks at another woman; Shinobu isn't sure if she's been jilted or she's been saved from a life of misery; his Lum-crazed schoolmates are plotting to get him "out of the way"; and his parents are loudly wishing he's never been born.
And that's the setup to Japan's all-time favorite Anime TV series, one that lasted almost 200 episodes, plus 6 movies and 11 OVAs!