After a fight with Ataru one night, Lum goes up to her UFO. As she sleeps, her ship crashes on Mendou's estate, and she has lost her memory. Mendou later tells Ataru that Lum is now staying with him, and will fight to keep her there.
Lum keeps crossing into the wrong parallel dimensions, which all lead her to Tomobiki and Ataru, yet exist under far different circumstances. She hopes the next dimension and the next Ataru are actually the real ones.
Ryuu has stopped wearing her chest warp, and is noticeably bustier to her classmates. Of course he boys on her rugby team are eager to grope her during the game. A tiny, rugby ball-shaped UFO arrives, and takes Ryuu, Ataru and Lum on board.
Ran visits Oyuki to complain about the Neptunian lemmings which ate her food for Rei. Ran later discovers that the lemming leader aboard her ship, eating everything in sight. Oyuki makes a surprise visit to Earth, searching for the lemming.
Lum and Ataru visit a pet shop which has a cow among other things. The cow bites Lum's hand, and later she discovers that her horns have grown long like a cow's. She then fears that she is slowly turning into a cow.
Megane's directing a movie, and asked Mendou, Shinobu, Ataru and Lum to participate. Prior to filming, he individually pitched to them wildly different storylines in order to get them on board. What is this film really about anyway?
Princess Kurama is back, and now she's set her sights on Rei, much to Ran's chagrin. Kurama's taken Rei away, and Ran enlists a reluctant Lum to travel to Kurama's place to get him back. Kurama has no idea that Rei can turn into a tiger-cow, and her crow underlings desperately try to keep her from ever finding out.
After a high school student is bullied by Soban, Lum intervenes. The girl then sets a fight between Lum and Soban. Lum, realizing that she does not have the strength to defeat Soban, decides to 'cheat' by using strength-enhancing drugs.