Lum finally has to confront that Ataru might actually leave her, and the show strips away every joke to prove it matters. The romance stops being punchline fodder and becomes the entire point, this is what happens when a gag manga discovers it has a real heart. An 11-year-old alien girl's wedding invitation becomes the thing that forces Lum and Ataru to say what they've been dancing around since the series started.
Ataru's casual childhood game of tag becomes a cosmic catastrophe when Elle, an alien princess, arrives to collect on an ancient marriage contract. On her homeworld, stepping on a girl's shadow during their game sealed his fate: he's engaged. The wedding invitations have already been sent, and worse, Lum isn't on the guest list. Predictably, Lum goes nuclear. Her electric attacks prove useless against Elle's protective barrier, leaving her fuming and desperate. When diplomatic attempts fail, Lum takes matters into her own hands. She and her friend Benten orchestrate a plan so outrageous it borders on brilliant: abduct Ataru and everyone invited to the ceremony, turning what should be a formal alien wedding into absolute chaos. What follows is a wild chase across space and time, with Ataru caught between an alien bride he never agreed to and the demon girl determined to stop the wedding by any means necessary. Expect ridiculous obstacles, explosive action sequences, and the kind of romantic comedy mayhem that only the Urusei Yatsura universe can deliver.