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 childhood game of shadow tag turns into a cosmic problem when an emissary from Elle, an alien princess, comes to arrange their marriage. About 11 years ago he stepped on her shadow and won, and on her planet that means the two must wed. Invitations to Ataru's wedding reach everyone in Tomobiki, and Lum is not named as the bride. Predictably, Lum goes ballistic, but a force field now shields Ataru from her electric shocks. Her friend Benten proposes beating Elle to the altar with a wedding of their own, so the pair abduct Ataru along with every wedding guest. The stage is set for a chaotic sci-fi romantic comedy showdown over who gets to marry him.