>>1714The story and setting got re-written since they didn't have a plan and just responded to what worked and what fans seemed to like. The early premise seems to be Ataru and Shinobu (remember her?) being accosted by Urusei Yatsura on a weekly basis when they just want to get on with their lives and get married. Lum was just going to be a recurring harlot who is trying to break them up because she wrongly thinks that Ataru is engaged to her. Then the story was retooled to be about Lum and Ataru being together with Shinobu as the side character.
Then it was retooled AGAIN to focus mostly on Tomobiki high school - making it the prototypical high school anime. Characters like Sakura, Mendo, or Ryunosuuke have nothing to do with the original premise, but they end up taking a majority of screen time once they're introduced.
Rumiko's later works were more planned out with a more consistent premise because she and her team had more experience in what fans wanted. If they knew how the series would play out, UY would probably be a supernatural series with no aliens centered on the high school and town from the get go. Other than electricity and flying around, the fact Lum is an alien is irrelevant for 75% of later UY stories. Could have easily made her and the Oni come from subspace to begin with.