Local Wei Wuxian did not intend for his notes to be used as a basic guide on cultivation so nothing is laid out in neat reasonable ways.  Some of them are notes on ideas in progress and contain theories that are later confirmed or dropped; Wei Wuxian did not timestamp his notes or put them in chronological order at any point, and also didn't often go back and add notes to his personal notes if a theory was later invalidated. 

There's a page mentioning that Jiang Cheng is getting frustrated with how few of his cultivators have formed their golden cores, even though they both know it takes four years on average - not everyone is as fast as them!  They are formed in the lower dantian.  It definitely involves meditation, and needs instructors to watch over them as they do it "so the kids don't make their cores upside down just because they can't see what they're doing yet."

Wei Wuxian makes occasional references to learning techniques but he doesn't go into detail on something so obvious to him.  There are no references to learning a technique then not being able to use it.

"For concerns: Demonic cultivation is similar to using talismans in being too difficult for the mundane to learn, due to senses needed to see energy only granted by a golden core even if one isn't needed for its use," is written on one page otherwise dominated with sketches of decorative tassels.

Possible theories for rebuilding golden cores in people who had theirs destroyed are circled around to multiple times but don't seem to have gotten anywhere.  "sending Jiang Cheng off to see Baoshan Sanren is a trick that would only work once, and there might be others around somewhere who can be brought in."  (Because Local Wei Wuxian does in fact know that Jiang Cheng can read his note-taking handwriting and might one day do so.  You just don't leave incriminating notes around!  And local Wei Wuxian knows what he means.)

Memorizing lots of techniques makes someone more versatile!  But apparently most cultivators find this hard.  There's a reference to "the usual set everyone in Yunmeng Jiang learns," but not a list of what that is.  Methods for communicating with ghosts, exorcising harmful spirits, and purifying areas are mentioned at various points and can be assumed to be included.  Also lots of sword fighting techniques, some of which sound like magic. 

He is not expecting a basic guide on cultivation (maybe he should have asked other Jiang Cheng for an actual basic guide - though maybe other Jiang Cheng would have told him to focus on his report or told him off for trying to pry into secrets - but he didn’t). And he knows what his notes are like. This is what he’s got! (On the bright side the notes are not likely to contain really stupid theories by overly important doms!)

The notes on golden core formation sound very ‘yep, learning power stuff’ to him. Ha, he was faster at local power use too. And so was other Jiang Cheng - what with local power use being what other House (sect) Jiang does, naturally he was. Was he faster though?

...apparently Baoshan Sanren is in some way an entity you can currently go see here? ...Ok he has no idea what that entire note means. 
Also apparently golden cores can be destroyed, which feels very weird! Other Jiang Cheng did say they were an organ or something like that right? And they’re in a place. Which is also really weird!

This is not going to be enough to let him definitely distinguish between his theories, though he does come up with some more theories and updates in various directions to the previous ones and acquire a bunch more material for his own not especially neat notes.

(He is guessing that, given other Jiang Cheng accusing his flute of evilness, the flute-playing-for-controlling-‘resentful energy’, and that name, that demonic cultivation might be the flute one.)

Wandering around the room with a sheaf of notes (he’s limping less now, though still some - Lan Zhan might have scolded him a bit, but he has been being (mostly) still for a while today, ok) his eyes happen to fall on the fruits other Jiang Cheng had left. Oh, yeah, fruit breakfast, he should eat those.

Somewhat later, finished with a set of notes, he sees and remembers about the fruit again. Right, food! This time he gets all the way over to the fruit. Are they at all interestingly alien fruit? Historical fruit? Somehow-affected-by-different-power-use fruit?

Historical fruit!  If his world has the same flora as Earth he will be able to recognize the approximate genus of the plants if not the specific cultivars - persimmon and pear and so on.  They're far from wild but have had fewer iterations of selective breeding than he might be used to, their seeds a bit larger and more numerous.  There's nothing magical about them.  Lotus Pier harvests its eponymous lotus but other than that cultivators don't do much in the way of farming food and farmers don't have magic. 

At some point in the morning a servant crosses through the courtyard to deliver supplies to Jiang Cheng's room, but they have no reason to pass particularly close to Wei Wuxian's door. 

(Unless it happens sufficiently loudly or sufficiently magically-with-a-range, Wei Wuxian is going to have no idea of what is or might be happening beyond his door.)

'Fruits and their cultivars and history' happens, in fact, to not be one of the random areas he knows much random amounts of information about. It's not obviously alien fruit, like sparkly crystal fruit or coiled-spiral fruit - probably predictably, given everything else, and also he would have noticed that earlier. Coming all the way up close and picking up some fruit fails to reveal any more subtle obviously alien fruitless, and it turns out it's kind of hard to tell the difference between 'same basic fruit but different because historical' and 'different fruit but similar because fruit evolution'. But it is different from the fruit he usually has, which is neat. (He does check it all for magic - he's not expecting magic fruit that much, but if it is magic fruit he's definitely not going to miss it!)

He munches on some fruit wandering around the room some more, then comes back to sit on the floor against the bed, tosses his next fruit up and catches it before taking a bite. The picture of Lan Zhan from other him's notes has ended up face up partially on the pillow at some point; he smiles at it with his next bite of fruit-breakfast.

...and then it hits him, really hits him, that from the point of view of everyone back in his own world he vanished into thin air or bizarre magic out of his room at music camp, and no one is going to know where he is or what happened to him or be able to find him if they look for him.

He swallows. (He isn't actually sure if there's fruit in his mouth or not). Fuck. 

He - has no idea one way or the other if the nonvolitional-and-it-turns-out-interworld teleportation left any trace from the other end, or even if it did how long a trace would last. If there's no trace - the music camp is going to think he's snuck out, again, and look for him or wait for him to show back up. He can't remember at which point in him not showing back up they have to tell Jiang Cheng, but at some point they're going to have to tell Jiang Cheng.

Who will probably think he snuck out and then got into something stupid. Or else is going to think he's actually run off. - That's fine, really, it's not like a bulletin about him being a runaway is going to do anything to him while he's here and he didn't run off and he can prove it. 

He closes his eyes and feels like he can still see that picture, see his own Lan Zhan's face. Lan Zhan. Someone is going to tell Lan Zhan, and Lan Zhan will think he - just decided to do it, and didn't even talk to him first, didn't even tell him first. And - his Lan Zhan is too good to him, always thinks better of him than he deserves, his Lan Zhan is going to think he must have had a reason, must have had a good reason to suddenly change his mind so much and then just go ahead and do it right then. (Lan Zhan - Lan Zhan has to know, right, he wouldn't just disappear, he wouldn't just leave him, that if he did suddenly decide he had to get out that he'd find some way to contact him, somehow, just as soon as he could...) 

If there is a trace, if it's as what-is-this as what he got from his end - or even if it somehow isn't - no one's going to think he did that. (OK some people might think it a little. But not really, not for real). So everyone's going to think he was kidnapped, by someone with fucking teleportation. 

- Lan Zhan will worry so much. He wants to hope it's the other one, just for that. Except Lan Zhan will worry about him anyway, even if everyone says he ran off will worry he actually snuck out and ran into something, will worry about him off being a runaway submissive, will think he had a reason and will worry about what happened.

Shijie will worry.

(His Jiang Cheng will worry. If he got to see that he'd expect to find it somewhere behind 'wanting to fucking kill him' (not literally) in the first case and 'wanting to fucking kill whoever took him' (absolutely literally) in the second case, but - he does in fact know that.)

(Uncle Jiang will - think he's failed in his duty to his parents. And worry.)

- He tries to remember what the betrothal rules are. How long are the terms if something happens - does it matter if he's a suspected runaway, if it's different does there need to be proof, does it matter if it looks like something happened but no one can find him -.

It has to be a while, that's how contracts like this work. It has to be a while, so no one's going to be trying to get Lan Zhan to marry someone else, because he can't just be gone for that long anyway, that's too long, Lan Zhan will, Shijie will -

He draws his knees up to his chest, puts his arms around them. Maybe everything's fine, really, and this is one of those interworld travel setups where time doesn't pass in his world while he's here and when he comes back no one will even know he was gone anywhere. Or time passes really slowly and it'll have been an hour and one of the doms will be yelling 'Wei Wuxian, if you're up there again -' into the attic with all the abandoned instruments.

What if it's the other way around and even if he and other him figure out the way back really soon it'll have been a hundred years -

He sits up, sets his jaw. No, absolutely not. He does not care what interworld travel rules turn out to say, that is not going to happen. He's in another world, so he got here, so that happened somehow and it's possible, and he's got two worlds' power use systems, and other him is holding borders and invented a whole new form of cultivation, (and he knows he understands computational power analysis better than at least half the doms who get themselves published about it, and that's not counting what he hasn't even seen published anywhere). They're going to figure out this interworld transportation, and if time thinks it should have been a hundred years he's going to invent a version with time travel, and if that's not how interworld travel is supposed to work then it can go and drown itself in a lake and he's going to get back to his Lan Zhan. 

He stands up. (The fruit, partially eaten, ends up somewhere by the bed, and he has basically forgotten about it.) Stacking up a pile of other him’s notes, he heads for the desk, where he applies himself to the pile with a new line of fervor.

For the next while, the room will have no activity other than Wei Wuxian absorbed in the notes with Wei Wuxian intensity, mostly at the desk, occasionally pacing again or in some stranger position.

He first notices that he has a problem when on his latest turn of pacing he - must have gone higher intensity pacing without noticing it - and sets his foot down hard enough to jar his ankle. That gets him a jolt of pain strong enough to get through his (currently extra heightened!) threshold of ‘ignore all that’ and stumbling enough he almost trips onto the floor. Ow. He lifts his foot and bends down to rub at his ankle. (Yep, Lan Zhan would definitely scold him. And help him kiss it better.) (- Nope, no sadness, he’s going to get back to his Lan Zhan and tell him all about his other world adventures.)

Alright, he maybe needs to take a break with the pacing. He goes back to the desk, sits down to refocus on the notes.

Refocusing on the notes turns out not to work very well.

Sitting back at the desk also turns out not to work very well. He wants to get up again immediately. He wants - 

He moves two notes, picks up another page. His brain does not cooperate with the next step of the process. He feels like there’s a wire running through him, through his body and his head. He wants to get more up then getting up.

- in retrospect now he can notice this is one of those been-building. Yep, here are his more recent notes gaining more doodles escaping the margins as they go on, drawings getting more aggressive. If he’d been using ink he knows his brushstrokes would have been going everywhere. As it is he may have almost dragged a hole through his paper. His pacing didn’t leave that kind of physical evidence, but while his ‘noticing stuff while absorbed’ is, exhibit one, possibly not so great, his ‘what he did ten minutes ago’ memory isn’t that bad.

Kind of unfortunately, he is now not too absorbed to notice stuff. 

He wants to get up, he wants to get more up than getting up, he wants to walk - he wants to walk and keep walking.

He does stand, paces a round across the room, favoring his other leg. He turns at the wall, he turns at the other wall, at the bed, at the door. He wants to walk and keep walking, he wants to walk through the wall, he wants to shove himself through the door if he has to. 

The walls feel like they’re kind of closing in on him again. He wants to jump out of his skin. 

He throws himself down on the bed (gets up again a few seconds later). Ah, fuck. - It isn’t fair, he’s not even standing at a wall or anything, it’s not like he’s having to copy horribly boring etiquette lectures, this is other him’s magic notes that’s as much directly opposite from boring as you can get!

(He tries to pick up some notes again and do something beyond the step of looking at the piece of paper and wanting to jump out of his skin some more. This continues not to really work at all.)

- And it would be fine if he could walk and the door wasn’t in the way. If the air was moving, if there was something to see and listen to, if he could do something, if he could talk to someone - he doesn’t even need to actually do it. He is 100% confident that if he were looking at these same notes sitting on the roof everything would be working just fine. Unfortunately -

He knocks his head back against the wall. It’s not like he doesn’t get confined to his rooms all the time at home! But - first of all his rooms are bigger, which he doesn’t usually think about in this context but apparently turns out to matter. And have his belongings in them, some of which he has on some level selected to be good for this kind of situation. And he’s usually allowed out in the courtyard. And sometimes even allowed very specific phone privileges, or to talk a bit to the servants. And usually he does not have to be quiet on pain of execution-worthy political problems for people around him, so if he decides to turn cartwheels while singing themed credits music the most that’s going to happen is someone shows up with a ruler.

- And generally when he’s confined to his rooms he’s had his hide tanned first, which he also doesn’t usually think about as an important factor but also clearly turns out to matter.

(And if he really does need to (also if he doesn’t) he can in fact go ahead and just leave, and if he doesn’t get caught that’ll solve his problem, and if he does get caught that’ll solve his problem a different way.)

He glances at some of his doodles as he goes past the desk again. Note to self, next time you get transported to another world make sure you spend the preceding several days running around and climbing random buildings you’re not supposed to, and not sort of partially behaving yourself at music camp, maybe that will help!

- Well. He’s not going to get anywhere by complaining inside his head, is he. 

(There isn’t any question that he’s going to stay in the room and quiet. (Maybe some doms who’ve ever met him would have their doubts, but some doms just really really think that subs obeying whatever rules they came up with is literally the most important thing in the universe.) It would sure be nice for him if he got to help out local Jiang sect by taking a beating or something (he’s great at that!) but sometimes life isn’t nice like that!

Unfortunately, among magic he has not invented, there would be ‘fast forward things because you already know what’s going to happen.’ So instead he still has to be here the entire time.)

He goes over to the door again, checks the dissipating part. Recalculates. Right. That’s how much time he’s got left, and after that probably other Jiang Cheng will show up again. …If not he is going to replan when that happens.

(He feels like there is something running under his skin.)

He paces back and forth across the room again. He jumps back and forth across the room on one foot (just the one, not the other one). He does some (quiet) physical exercises. He bites down really hard on one of his fingers.

He considers if this might be a good time to look into other him’s porn collection - or same thing minus the porn collection - but he is not actually in mood and also other Jiang Cheng keeps walking in on him and he has read enough intercultural contact to remember that sex things is one of those places you really need to check the rules first if you don’t want all sorts of new and not usually exciting problems.

He does some more physical exercises. He picks a random object in the room he can throw and some random locations he can aim for and tries to get the one into the other. 

He tries writing about his world’s power use because other Jiang Cheng is probably going to want to see it when he comes back. Very nonsurprisingly this doesn’t go very well. He gets some notes down but no part of anything even slightly resembling a Proper Report. 

He crumples up a piece of paper and throws it across the room. He goes after it.

(It’s very tempting on some level to just - do something to the door enough to set off the whatever it was, and hope it was something like shocking him and not something like paralyzing him or else that other Jiang Cheng showed up to actually thrash him this time. He’s not going to do that though. He’s going to try not to do that.)

He does some more exercises. He bites down hard on his finger again. He eats some more fruit. He makes a paper airplane and tries to toss it around the room.

Meanwhile, Jiang Cheng's day has been fairly typical other than the constant worry in the back of his mind about having left a Wei Wuxian unattended.  This turns out to take a surprising amount of his concentration, leaving him occasionally staring blankly at the person in front of him and having to ask his second in command for his opinion under the guise of testing him so Jiang Cheng doesn't have to show how little he was listening by having to ask them to repeat what they said.  It's good practice for his second, anyway.  The man is not Wei Wuxian, but other than not being the second that Jiang Cheng wants he is adequate enough at the job.  It's good to know that things won't completely fall apart if he steps away from Lotus Pier for a day.  Not that that will stop him from worrying.

In between scheduled meetings Jiang Cheng re-arranges his next few days to free up time for a short trip.  An elderly scribe nods approvingly at Jiang Cheng's claims about taking some time to meditate more deeply than the brief hourly sessions will allow.  He'd considered claiming to go on a night hunt, but those are kept track of and a Sect Leader isn't permitted to hunt without backup anyway.

It's getting into the afternoon when the last of the meetings end.  Jiang Cheng still has to look over the most recent drafts of some documents, and there's reading he'll want to look into regarding the comparative advantages of whether or not disciples should have to learn separate fire and light talismans... but as long as he gets to them by the next morning it doesn't matter exactly when or where.  He packs the relevant papers up and takes them with him.

Jiang Cheng takes a walk through the nearby marketplace to pick up supplies and food.  Favorite foods of the local Wei Wuxian, specifically, since how dare anyone imply that Lotus Pier is not completely welcoming (even if that person was sort of Jiang Cheng himself.)  Careful tucking things away in his qiankun pouch whenever he isn't being looked at and it isn't hard to get two people's worth of various dishes and jars of two of the better wines.

Black and red things are on sale here and there.  Jiang Cheng's hands itch to pick them up but it would be too obvious that he wasn't buying them for himself.  Instead, he finds the needed supplies for Wei Wuxian in purple and blue and the gray woods that match them.  It isn't hard - the town beside Lotus Pier has nearly as many lotus-carved things as Lotus Pier itself does.  

Eventually, he reaches the end of the market and loops back.

Jiang Cheng looks every which way as he crosses the courtyard of his house.  Left and right, at all of the corners between the buildings, and up on every visible roof.  He shut and locked the main door leading to the courtyard from outside as soon as he passed it, which should deter most non-emergencies.  He makes it to his room unaccosted and picks up a small table and a pair of cushions after a mental debate with himself whether or not it would be worth it.  No- he can carry a table a few meters quickly and quietly, and he'd rather not eat on the floor.  If anyone sees him and asks, he's using Wei Wuxian's old room as a storage space for excess furniture.  He slides the heavy furniture under his arm and walks towards where he last left Wei Wuxian.

The coast continues to be clear.  He knocks, but after a moment's notice tries sliding the door open without waiting for long.  Catching a glimpse of Wei Wuxian changing or something would be embarrassing, but significantly less bad than Jiang Cheng getting seen waiting at that particular door.  Besides, there is a latch on the inside if Wei Wuxian wants to keep him out.

The alarm he'd placed on the door is running low on power but is still there.  The second the door moves, the tripwire releases and pelts him with the vague yet unmistakable sensation of been-sent-a-message-that-says-nothing.  

Jiang Cheng startles and lets out a quiet yelp.  He only barely manages to catch the table as his arms try to flail upwards in defense.  Cultivator reflexes let him catch it before it strikes the ground.  It leaves him in a somewhat undignified posture of having to hold the table partially with his knee as he gets it back to a stable carrying position.

Sheepishly, he opens the door the rest of the way and quickly shuffles in.

Is Wei Wuxian there?  Did he see and is now going to laugh at Jiang Cheng?

He’s going back and forth across the room again when he hears the knock. Huh, other Jiang Cheng is knocking this time! …Orrrr that’s someone else. 

…He should super have come up with a plan for that ahead of time. And also asked other Jiang Cheng. Great timing for thinking of that, Wei Ying!

Options in the room (he’s pretty well acquainted with the room by now). He’s not going to fit in or behind the clothing trunk. Not the kind of door he could stand behind at all. 

Really just the one option here (hey, it’s better than just standing in the middle of the room!) As quickly and quietly as possible, Wei Wuxian is going to drop and then roll himself under the bed, trying his best for an angle where he won’t be visible from the door but he can still see out. (Having left the blankets partially draping over the side of the bed is going to help him here.)

(He does hear some sounds from outside, but is not going to be able guess what they’re corresponding to.)

It's a good thing that Jiang Cheng was already reaching for his newly restocked privacy talismans with his free hand when he notices that the room is empty, because upon finding that Wei Wuxian isn't in sight Jiang Cheng is going to throw a very loud tantrum.  And also the table.  There is a crash as the edge collides with the clothing trunk, then another as it smacks onto the floor upside down. 

This Wei Wuxian wasn't a cultivator; not only should he have no way of getting past the alarm but he wouldn't have even been able to see it to try to get around it.  That meant the most likely thing was him vanishing back to his own world.  Good for him.  But that means that Jiang Cheng is never going to know anything more about it.  He had lost his entire chance because it happened when he was required to be elsewhere, because the universe hates Jiang Cheng specifically, and Jiang Cheng is going to wordlessly scream about it while throwing the cushions at the wall.  One lands on the bed.  The other bounces far enough off of the wall to land on the floor, and Jiang Cheng picks it up and flings it back at the wall again until it lands on the bed with the other one. 

Then he stands there and stares at the wall.

Things you get out of looking down a lot, he can absolutely and with no trouble recognize other Jiang Cheng by his shoes and the hem of his robes. Yep, that's other Jiang Cheng.

Aaand fuck. Apparently with all the repeated total shifts in what he knew was going on here/what was actually going on, he'd kind of stopped thinking about how other Jiang Cheng does things like this! (He has - kind of flinched partially into a ball. Why does he even have that reflex, it's not like doms throw furniture at him a lot.)

Fun fact, doms yelling and throwing furniture turns out to be so much more affecting in real life than not real life.

Well, his nervous system is still not helpful and he's still got his foundation and other him isn't dead and this room doesn't even have glass windows or cast iron pans or anything, so he's totally fine and has nothing to worry about! And if other Jiang Cheng is going to throw furniture at people and not just other furniture, then here he is, definitely the right person for that.

He is going to just wait here a little until other Jiang Cheng isn't throwing furniture right at that moment, that sounds like a good idea. The room doesn’t have much furniture.

The silence is very silent. See, great timing Wei Ying! He gets out from under the bed. This feels like probably a kneeling then talking situation. He tries to kneel very quickly.

"Wei Wuxian!"

Jiang Cheng is filled with relief that other Wei Wuxian is here and safe?  Embarrassment at having been caught throwing a tantrum?  Anger at Wei Wuxian for hiding from him.  That must be it.  "Why are you always playing games?"

The cushions are on the bed but he's standing close enough to grab them.  He peevishly decides to pick one of them up and throw it at Wei Wuxian's back when he's still crawling out, then pick up the other and start bopping Wei Wuxian repeatedly with it.  They are pillow-like and full of fluff so this does very little to impede Wei Wuxian's movement.

- there, see, cushion, very nice thing to have thrown at you as things to have thrown at you go. (He already flinched at the flying object before he realized what it was.)

He braces a bit when other Jiang Cheng comes closer to him. 

…?(?) It takes him a moment to figure out what is physically happening, and that does not really help him figure out the more important questions like ‘what is other Jiang Cheng doing, what’ and ‘is this the sort of thing where he’s supposed to do something and also supposed to know what it is.’ …ok, when doms are doing things to you usually they want you to stay there and other Jiang Cheng getting so close feels like other Jiang Cheng wants to make the decisions here. He stops trying to finish getting out from under the bed or to his knees. 

“I’m sorry, Sandu Shengshou, I wasn’t sure it was you when I heard someone.” He’d mostly stopped expecting physical reprimands before, though on some level he was really still expecting them. What he can expect now sounds like the thing he is about to find out.

(Part of his brain is wondering if this is the kind of place where everyone thinks screaming and throwing furniture is just totally fine for doms to do, or if it’s more the ‘you really shouldn’t but of course it happens sometimes, everyone understands that’ kind. …If it’s the second one this is still probably going to be really awkward later but how about he deals with that when later happens.)

When Wei Wuxian just lies still and stops moving, Jiang Cheng backs off.  At first he's hurt at the rejection.  He wants to pull Wei Wuxian up again and demand answers.  Why aren't you fighting back?  Why are you ignoring me?  Then he remembers that this isn't his Wei Wuxian.  Caught up in his panic and emotions he'd forgotten - it was so easy when they looked identical to each other.  This other dimensional Wei Wuxian is serious and formal and strange, but that might be for actual logical reasons, not terrible demonic cultivation reasons.  Reasons like wanting to be a proper guest. 

Now what is the proper formal thing to do in response?  Does Jiang Cheng have to apologize?  Damn it.  He really hates apologizing.  The cushion is tossed onto the table, which is very sturdy and survives the impact with the cushion just as well as the collision with the wooden chest.  Only slightly belatedly, he throws a privacy talisman onto the wall behind him.  After that, there's nothing else he can do to put it off.  Jiang Cheng braces himself.  If this Wei Wuxian wants formality, he'll get formality. 

"Jiang Cheng would like to offer apologies for mistaking you for h- for the local Wei Wuxian.  Such a display was unbefitting and does not reflect the intended hospitality of the Yunmeng Jiang Sect to its honored guests, even in these unusual and limiting circumstances."  His bow is perfect and precise, and he even manages to keep from sounding sullen.  He has had a lot of practice since becoming sect leader.

(Part of his brain has continued on wondering things, like, if doms throwing furniture is ok here, do other doms he knows also do that? …He cannot imagine Lan Xichen throwing furniture. Even if doms were supposed to throw furniture all he can imagine is Lan Xichen picking it up carefully and setting it somewhere else. Grandmaster Lan would totally throw - not a book. Something the same size as a book. Probably at him personally if he ever sees him. He’s kind of worried about Lan Zhan’s father now. Wen Qing does not feel like she would throw furniture. …Heee wouldn’t put it past Wen Qing’s relatives to throw furniture in his world.)

Ahh shit ahh shit. Right, really obvious in retrospect, no prize Wei Ying, just because it’s fine enough here to throw furniture around your submissives doesn’t mean it’s fine here to throw furniture around other people’s submissives. He scrambles the rest of the way to his knees, gets himself into Good Proper submissive kneeling. …Now he also has to do etiquette, pout. (He does not actually make any Impolite facial expressions because he is representing House Jiang here). He bows.

”This one knows that the House Jiang of his world knows the value of and gives gratitude for the hospitality of the Yunmeng Jiang Sect, all the more so in these unusual and limiting circumstances. This one knows that House Jiang desires good relations of harmony, honor, and benefit, to House Jiang and to the Yunmeng Jiang Sect.”

…This is still sort of his brother, he doesn’t have to be completely all etiquette, right? (May be getting himself finally whacked across the hand or whatever it is they do here, but if not getting whacked across the hand was his priority very much, his conversations with doms would go very differently!)

“- He won’t be super mad, Sect Leader Jiang. He’ll accept the apology. I’ll talk to him.” Local Jiang Cheng might recognize a flavor of Wei Wuxian smile. “Ah, he’ll probably think to himself it might be good for me.”

Jiang Cheng didn't study for alien etiquette and he hates being unprepared.  That doesn't mean he's going to let Wei Wuxian beat him at it.  ...Should he be letting Wei Wuxian kneel during this?  Eh.  He doesn't have much choice - manhandling someone up during an apology for attempting to roughhouse would only show he didn't understand his lesson.  Besides, if people were supposed to be standing to receive apologies in the other world it is Wei Wuxian's job to know it and not Jiang Cheng's problem if Wei Wuxian fails to. 

"Yunmeng Jiang also values and wishes for good relations of harmony, honor, and benefit between House Jiang and the Yunmeng Jiang Sect.  Peace and the opportunity to strive for mutual understanding are goals which the Yunmeng Jiang Sect desires, both between the Yunmeng Jiang Sect and House Jiang, and between our two worlds." 

That seems like a good enough sentiment even if Jiang Cheng isn't sure why Wei Wuxian is bringing up inter-world relations right now.  Is it part of the standard response for an apology or a change in subject?  Sure, Jiang Cheng had invoked his entire sect, but Wei Wuxian is being hidden in Lotus Pier.