Six-year-old Ataru steps on Elle's shadow during an impromptu game of shadow-tag; in Elle's culture, this is viewed as a marriage proposal. Eleven years later, Elle returns to Earth in order to marry Ataru — by which time not only had he forgotten the events of his childhood, but he was also going out with Lum. The rest of the plot focuses on Lum's attempts to prevent the marriage. The film was directed by Mamoru Oshii who was mad at the many requests that the producer made of him to alter the movie. Rumiko Takahashi considers this film her favorite and it is the most true to the original series.

As the perpetually lecherous Ataru and his friends prepare for a carnival at Tomobiki High School, they gradually realize the days are literally repeating themselves. Any effort to break the pattern dumps them back where they started.

The third film finds Ataru transformed into a pink hippopotamus, which sends Lum chasing after the wicked magician responsible, with catastrophic results. With Lum gone, her friends decide that there is no reason to remain, and so Tomobiki slowly returns to normal. The highlight of the film is a high speed chase scene with an angry Lum flying after the mysterious Ruu through the city at night and into a hall of mirrors (and illusion ). Ataru's true feelings for Lum are probably more obvious in this film than any of the others.

While performing in a student film, Ataru cuts down Tarozakura, a large, ancient cherry tree. Strange things begin to happen all across Tomobiki: a mountain appears out of nowhere, spring changes to winter, and Lum loses her powers, while those around her act as if she doesn't exist.

It seems that Lum's grandfather made an agreement that should he have a daughter, she would be married to a traveling merchant that he met. Now, the merchant has come to collect due. Ataru is tricked into thinking that Lum wants to leave, and so, in a moment of anger, says he hates her. Arguments erupt, and Lum decides that she must know the truth of Atarus feelings. As for all the questions of importance for the Onis, a game of tag begins, one that Ataru can win simply by telling Lum I Love You. However, in the end his pride may end up dooming him. So begins the series of events that will at long last decide the future and fate of Ataru and Lum.

Lupika, an alien princess, is in love with a tofu seller. To make him love her too (at least, announce his love. He obviously fears the social taboo of a tofu vendor marrying a princess), she needs to get a love potion, which is in a certain temple. Legend has it that the only person that can obtain this love potion is the most lecherous man in the universe. That man turns out to be Ataru Moroboshi. Lupika kidnaps Ataru to make him get the potion, and Lum and her friends go out to search for Ataru.