When everyone in town receives invitations to Ataru's wedding, they are shocked to see that his sweetheart Lum is not the bride. Eventually they learn that when Ataru was playing games as a...
A curse placed on Lum as an infant manifests itself in the present day, causing her to be taken to another dimension. Lum's husband, Ataru Moroboshi is turned into a hippo, and attempts to find Lum with the help of her friends.
Ataru and Lum must replay their fateful game of tag to decide the fate of Earth, that's being threatened by giant space mushrooms, as well as their relationship.