When an invading race of oni sets out to claim Earth, the unlucky and incurably lecherous Ataru Moroboshi is picked at random to decide its fate in a week-long game of tag against Lum, the invasion leader's daughter. Ataru wins, and when he blurts out talk of marriage in his excitement, Lum takes it as a proposal and moves in as his self-declared wife. Chaos keeps escalating around Ataru, the lightning-throwing Lum, and his exasperated girlfriend Shinobu.