Oldfan:
Warning - this theory will cross between the four mediums of Urusei Yatsura - the Manga, the TV Show, the Movies and one very specific OVA. It's a bit lengthy so sorry for the long post.
I was first exposed to UY in the 90s, I saw a VHS Rental of the 1st 4 episodes, and as I was getting into Anime at the time I figured I would give it a shot. To say the least, it became my favorite, but collecting it on VHS back then was really expensive. However, I did manage to get the 1st 16 episodes, half the OVAs, and all of the movies. I had no idea how many episodes there were but the overall theme was established - a crazy relationship with all the others around them involved to one extent or another.
Two years ago, I had found a YouTube channel that had ALL the episodes, at best at VHS quality but they were subbed and I'm not super fussy so after HOURS of using a website called KeepVid I had them all saved to a HD in my computer and figured one day I'd watch them all when I had the time. That time started in May of this year, and after a good bit of watching I knew a lot more about that 'relationship'. I now have all the Blurays from Japan, had to buy Only You on DVD since the movie on Bluray is cut by 10 mins.
All the guys love Lum, inclusive of Ataru, but he's too bent on being 'free' to commit to her. Lum doesn't care about any of the other guys, she's so in love with Ataru it almost hurts. But despite the efforts of others around them, anytime anyone gets NEAR her, he's all over them. The TV gives hints and nudges of this, but nothing more, while the movies actually establish the fact that he does love her and is willing to risk life and limb for her.
Only You - gets the ball rolling for them as near the end, Ataru realizes that despite how he acts, Lum cares only for him and he feels bad. (Doesn't marry her though at the end.) Beautiful Dreamer - Ataru admits he's in love with her, of course he admits to loving the others, but that falling sequence hits the one notion home, he really only loves Lum. Remember My Love - Lum at least will have a child, as Ruu is her descendant. Looking at the character of Ruu, he's precocious (something Lum was), he's headstrong and he has a bit of a temper. They never said who she married at the time because the show was still going, but there's another aspect of Ruu that gets ignored - the kid is a KLUTZ. Who else is one? Ataru, that's who. Plus, Ataru says he does things without thinking of the consequences, and Ruu did just that. It also emphasizes that if Lum is in danger, Ataru will do everything to get her back. He's also the one that remembered Lum after everyone forgot her, significance of cutting his finger on the soda can for the red string. Lum the Forever - Just reinforces the relationship - When everyone is fighting, Ataru goes jogging because he hates violence, he falls, sees the fog and calls Lum's name and immediately Lum knows she has to go back. The Final Chapter - There's a laundry list of tells for how Ataru feels, I'll mention some:
* Ataru goes into immediate action and bargains away ALL his girl stalking material to get her back * He thinks she's in danger and runs out the hole in the side of the school * He's genuinely hurt when he's fooled by the copy of Lum * His internal talk, does he have to tell her in words for her to know * Holding onto the horns at the end there * Honorable Mention: REFUSING to say he loves her because she won't know if it's the truth or notAlways My Darling - We'll just leave that one alone
The TV show had a bunch of well placed episodes that show how he feels, some based off the manga, but the rescue from Mendou's estate was not, and cemented one important thing. He'd run through tank and gunfire to get her back. And the very last episode with their kiss, it was annoying that we had to wait that long for it, but it was very sweet if not setup by that one MiB of Mendou's (my theory).
The Manga, which I only just got to read had similar moments, setting up relationship stories and such, but there was one manga story earlier on that didn't sit well with me. When Lum and Ataru went into the future and saw that Ataru was married to Shinobu and they had a kid. I had seen all the episodes by then and I didn't recall an adaption of that one. But since I wasn't too keen on the story, I didn't care so much. Then the Manga for Inaba the Dreammaker came (and the corresponding OVA in 1987). That story not only undid the prior time travel story but also setup the fact that no matter what Ataru did, he was going to fail at making a Harem. Even in his ideal dream, Lum leaves him if he does that. We then have the usual fight/chase in the OVA, and then they go through another door and it's a future they're getting married in.
The manga is a little less kind to Ataru as people are throwing things at him and everyone is objecting to their wedding, but he sees what's important. Lum is happy, even crying with tears of happiness and he knows that he has to save that future. In the OVA, there's no fight at the wedding, but the end result is the same. When the door is falling, he goes all out to try and save it. The OVA also gives us the ending sequence of Inaba finding Lum's "Sweet Home" doorknob and placing it on a door.
In The Final Chapter, because they were so bitterly fighting, the doors that represented their futures led to nothingness because if they didn't reconcile, obviously there was no future for them. Of course they did and we got the whole 'She get him to say he loves her even if it takes a lifetime' with his 'He'll say it on his deathbed'. And then we get to sit and wonder and basically have to say obviously she didn't leave him, she loves him way too much and he'd never let go because of the same feelings.
My theory (finally) is that while Inaba the character was supposed to be a bone for Shinobu (she lost Ataru to Lum and Mendou was obsessed with Lum - but failed), the story was a bone for us, more the OVA than the Manga, because of that doorknob sequence at the end. As someone that has wrote tons of stories in the past 30+ years, you can do the 'make it up as you go along' or have a planned outline of everything that happens. The idea was that they were all kids in school, enjoying their youth and living day to day, concerned with only having fun and adventures - why throw a marriage into that? We won't even mention that despite that Lum is one of the Oni, she has more human wants and needs than any other female in the show - period.
Fans, that's why. Say what you want, but other than Maison Ikkoku , every relationship created by Rumiko Takahashi put the readers/viewers through the wringer. To this day, I've found snippets of conversation on various websites that express a bit of bitterness that Lum didn't get her happy ending. But unless we're really lucky, we likely won't see it. Fumi Hirano (Lum's VA) is 62, Toshio Furokawa (Ataru's VA is 70), they aren't immortal and despite the fact they can both still do the voices pretty well (Look up Dallas Animefest 2016 on YouTube). So because this won't be revisited, Inaba the Dreammaker is our bone that says they get married and have a family (how many kids is up to you).
Seiryu:
Rumiko did mention at one point years back how she has like no intentions of making anything new with UY. While I would love something new for the goat series, I'm pretty satisfied with the way it ended. The real big question of the last storyline was really did Ataru care and was he so foolish enough to choose his own chaos over his love for Lum. We got the answers to both of those questions by the end. With that said, I do get what you mean. I too always saw the Inaba storyline where it showed the future of Ataru and Lum's marriage as Rumiko showing what would eventually happen between Ataru and Lum without actually needing to show the real thing.
Oldfan:
I don't know how reliable the source was, but I heard that the reason we got a new UY for the Rumic World in 2008 was because someone threw the equivalent of a boatload of money at Rumiko for an okay to make that OVA. Almost makes me wonder if there was enough of a desire, a good script and a real big sum of cash (again) if she'd approve of one last movie.
Wishful thinking I know.
I'd hate to see the day come if there was some kind of revival and the main two voice actors simply couldn't do it anymore because of their respective ages. I can only ever hear them as the voices they've been since Day 1. The English speaking dubs make my skin crawl.
Seiryu:
Agreed. New material would always be great in this series. I do wonder. This was after 50 years for an anniversary, wondering if they wouldn't mind having another one some time down the road. Cause there are quite a few stories I'd love to be animated (like the Ultra Colorful Pair Look).
Oldfan:
I'd be happy with one more Movie or longer OVA to tie it all up, while we still have the seiyū (声優) for Lum and Ataru with us, and by proxy Shinobu and Mendou with us.
By longer OVA, approx 60 mins not including opening and closing credits, a movie would be ideal since the idea of getting them from The Final Chapter to 'together' would likely involve their usual highs and lows.