It's so fun to toy with in my book. Time-travel tends to be my fix-it au's while dimension hopping tends to be my comparison pieces but they're both so delicious to me
When it comes to huntrix's relations to each other, the biggest difference would be that Mira and Zoey were told about Rumi's patterns way earlier, which allowed another level of closeness that canon!huntrix didn't get to have due to the secret needing to be kept.
But that is also basically the only one (very big indeed, but still) because Celine did encourage the girls to get close to each other. They needed to be close and trust each other when they were both on the field and on stage for things to go smoothly.
And this perfect world isn't perfect because Rumi's patterns are still very much fueled by shame. They are that purple colour and while she doesn't have to hide them from Mira and Zoey, she still needs to hide from the world. They're smaller due to the lack of shame from hiding them from her fellow hunters, but they're still very much not iridescent like C!Rumi's.
And something else is that Soo-min and Mi-yeong were very focused on helping them grow as people, putting duty slightly on the back burner. They saw hurting youngins and decided they were more important, something Celine couldn't do.
Celine turned them into hunters and idols, Soo-min and Mi-yeong turned them into people(at least from Celine's PoV. Unreliable narrator anyone?).
But being a well adjusted individual therefore comes at the cost of their skills. They're good hunters and fighters, don't get me wrong! But Celine looks at them and she sees rigidity and technicalities. They are technically perfect in what they do, reminding Celine so much of how she herself used to fight when she still had her own Soo-min and Mi-yeong to fight with.
But after they died she had to do everything on her own. She had to learn to be more dangerous, more skilled. It then translated into what she taught C!Huntris, making them extremely lethal. It meant that most demons that came through the tears in their world were nothing but canon fodder to them. au!Huntrix strategized and still got close calls where C!huntrix would have made a game out of who could slay the demons in the funniest way if put in the same situation.
Maybe that's how it starts lmao
Celine sees them out hunting at some point and Rumi -her fellow sword wielder- does something that's technically correct, but could've been done so much smoother, finally gets Celine to snap. They are going to die just like Soo-min and Mi-yeong had, just like Celine had at this rate! (is the excuse she gives herself. In reality it was honest to the Honmoon 99% reflex that caused her to shout-)
"Footwork Rumi! You do not slow down in a fight, unless you want to try tanking a blow, of course."
And it unfortunately distracts au!Rumi a bit, so Celine tosses her own blade at an approaching demon to banish it. Then she has to think back to all those lessons she gave years ago at this point.
"Think of the ground being lava. If you stay still too long you'll burn your feet, always keep moving." And she can tell this other Rumi is a bit annoyed with her backseat hunting, but she can also see her take the words to heart as she starts moving again, her feet carrying her along with each of her strikes, no longer staying in one place.
Either way it starts her down the path of coaching Huntrix once more. She doesn't have the time to re-train them, she needs to get home after all, but she does give them pointers when she can.
Soo-min and Mi-yeong will see this, see the familiarity and they'll ache. This is what they could've had if Celine had survived. They could've had her gently chopping Zoey on the top of her head when she tried to ambush her. They could have had Celine instructing the younger generation on how to keep their hair out of their faces when they fought (because neither Soo-min nor Mi-yeong let their own hair out when fighting), allowing Mira to finally do a simple half-up half-down style that wouldn't bother her as much.
(Also something something, Celine being in the middle of hunts and Soo-min and Mi-yeong actively panicking about it because of what happened last time their Celine was faced with a hoard of demons something something it doesn't help at all to see how dangerous she has become, it just highlights how different this Celine is something something Celine would also panic if she were to see them fighting demons something something)
And like you said: They won't see how Celine looks on with a burning throat when Rumi doesn't call out to them by name. Celine knows she's not made for that role, she knows that.
She'd grown too sharp in her time alone, she'd just cut anything that she held too tightly.
That doesn't mean it doesn't hurt.
C!Huntrix is fucking BESIDES themselves by the time they figure out how to get to the different universe. Celine might've been gone for weeks at this point, they had to lie and forge Celine's signature for the company so that they'd think she was just taking an extended vacation or something.
Add to that the first thing they learn in this new universe is that Celine is dead???? Yeah no. They are not having a fun happy time.
Maybe they come in through a tear or something, so other Huntrix goes to take care of it and. Well. Soon enough the Honmmoon is basically sending out a distress signal lol.
Celine is closest at that point so she hurries over only to see au!Huntrix taking hits from an enraged looking Rumi, fangs and claws out and everything; an angry looking Mira, who keeps glaring at her counterparts hair; and a strangely annoyed looking Zoey, who keeps tossing random shit she finds on the ground to mess up the trajectory of au!Zoey's shin-kals.
C!Rumi leaps at au!Rumi and is promptly snatched out of the air and held up by the back of her jacket like she's a misbehaving cat.
"No." Is all Celine says as she stands in-between the participants of the one-sided beat down.
in .3 seconds C!Rumi has attached herself to Celine in a koala hug and C!Zoey and Mira are actively leaping at her to join the hug because thank fuck you're not dead!
au!Huntrix is like ??? These are your versions of us???
And Celine is just like Yupp. These ones are mine.
au!Huntrix is left just staring as C!Huntrix is actively glaring at them from where they're clinging to Celine who... looks very used to being a human jungle gym.
(C!Huntrix recognized so many of the moves au!Huntrix were pulling and they were in fact Not Okay with Celine apparently taking the time to teach these posers things instead of trying to find her way back to the obviously superior versions. The audacity.)