I think it would be fun to do a "character swaps with older version of themselves" fic with Moshang. A post-canon Mobei-Jun who has been happily married for a while (probably at least 50 years old) accidentally touches some plot device artifact and time travels, swapping places with his 20ish-year-old self. Older MBJ wakes up in head disciple Shang Qinghua's bed where his younger self had been napping.
Younger MBJ lands in his own palace, where he is quickly found and fawned over by Older SQH, who can't help but think this MBJ is so cute. The System quickly confirms for Shang Qinghua that this situation has been sorted into a "multiple timelines" thing, so SQH doesn't have to worry about "protecting the timeline" by doing anything like hiding the fact that he's MBJ's husband. (So, there's an alternate timeline younger version of Airplane Bro now? He's just going to... ignore having an existential crisis about it. Yeah.)
Which is great because Older MBJ would not have thought about this at all as a potential issue. Older MBJ also thinks Younger SQH (Younger Airplane Bro) is incredibly cute and has no problem informing him that they're married in the future. Younger Airplane Bro is trying to figure what the fuck is happening, but he's having trouble thinking over the sound of how MBJ only became hotter: MBJ didn't get much taller, but he did get wider, heavier, more muscular, and hairier. Holy shit. Older MBJ doesn't even have any problems passionately kissing Younger SQH just to prove that they're married. And he smiles! He's so gentle and communicative! Comparatively!
("Luo Binghe is the Demon Emperor in my time," Older MBJ says. "Ah? Who's Luo Binghe?" Younger Airplane Bro lies very bady. "Hmmm, so you did know," Older MBJ says, and then makes some comment about LBH's husband that makes Younger SQH go, "HIS WHAT NOW?!")
Younger MBJ is trying to be cool, not really confused or scared, and Older SQH spoils him rotten by showing off the home that they're made together and how well the palace works to serve and defend MBJ. Linguang-Jun can't show up here because SQH will light him on fire if he shows his face. Younger MBJ doesn't even really like his SQH yet and is also struggling with how good Older SQH looks: a little taller, broader, relaxed and easygoing, answering all of his questions and explaining important things to him, dressed like a beloved demon lord's spouse, efficiently ordering everyone around. "Call me Gege," Older Shang Qinghua said with a wink, and it went straight to Younger MBJ's defenseless heart; he is developing new kinks immediately. Help him.
In the end, after a few days at most, they manage to switch Older and Younger MBJ back without too much issue. Older SQH is a little annoyed that his husband kissed an alternate timeline version of himself, but mostly because he sure would have liked that experience when he was only a disciple! Okay, SQH may have pet Younger MBJ's head and pinched his cheeks and hugged him and brushed his hair a little and shamelessly lavished him with good examples of human affection, but it's not the same!!!
Younger MBJ and Younger SQH in the alternate timeline are left in SQH's tiny head disciple house, completely flustered, sitting next to each other and barely able to look at each other. What. The. Fuck. Eventually, Shang Qinghua manages to say, "Uh, do you want to make out?" at the same time that Mobei-Jun says, "We should get married as soon as possible. Tomorrow."
