Urusei Yatsura: Movie 5: The Final Chapter (1988)

Things get very sticky indeed for Lum and Ataru when Lupa, one of Lum's many fiances, arrives upon the scene. All Ataru has to do is tell Lum he loves her, but that kind of honesty has never been his strong-point; however, maybe he will find some encouragement in the fact that the future of the planet lies in his hands, for if he can't win Lum's heart Earth will almost certainly be destroyed.