(Internal Lumine speech)
[Internal Aether speech]
The first thing Aether noticed was that something was wrong.
Yes, as awareness gradually returned to him, his senses reawakening, it was apparent that something had gone terribly wrong.
His body felt lighter, and his limbs slimmer than he remembered; he didn't sink as far into the sand as he used to, and the feeling of his braid resting against his back was absent…
Something happened to his precious hair?!
Aether stood up in a panic, taking stock of his surroundings. He was near the bottom of a cliff, on a tropical-esqe beach. The sun bore down on him from it's position in the middle of a clear sky. The sound of waves lapping against the shoreline intermixed with seagulls crying in the distance.
But most pressingly, this body which clearly wasn't his was wearing very familiar clothing.
[This is… Weird. This is really weird.]
(You're telling me. Why couldn't we be stuck in your body instead?)
And there was a voice in his head. Or their head, as he came to the rather shocking conclusion that he was somehow stuck in his sister's body, sharing it with her consciousness.
Aether sat back down on the sand.
[Lumine?! What in the name of… How did this happen?]
(Don't you remember? We were travelling, as we do, and that unknown god did something to us.)
[… Oh yeah… That cubic god.]
(… Cubic god?)
[Her powers were shaped like cubes, weren't they?]
(I guess… Anyway, can I get a turn now? I want to make sure you didn't break anything already.)
[Uh sure… I'll try to.]
By some mix of concentration and willpower, Aether relinquished control over his sister's body, his sense's dulling noticeably. The sensation felt oddly similar to shifting places with someone in a cramped space.
(Ahhh, it's good to be back.)
Lumine started doing stretches.
[So… Any idea how long we were out for?]
(Hours? Days?)
His sister shrugged her shoulders, filling Aether with the odd feeling of a limb that'd fallen asleep, only it was the entire body.
[Ugh, this is going to take some getting used to.]
(You're telling me. So long, privacy.)
[Oh yeah… Sorry in advance, Lumine. Hopefully this doesn't last long.]
His sister waved him off, even though he was still seeing things from her perspective.
(It's fine, that kind of stuff hardly bothers me. But knowing our recent luck…)
(Things are probably going to be like this for a while.)
A few days later, after adjusting to (or trying to, anyway,) the feeling of sharing a body, the twins decided to seek out civilization. After a few more days of journeying further inland, they caught sight of a medieval style city in the distance, intentionally ignoring the nearby cries of a monstrous sounding creature. That same day, they ran into the Outrider, Amber, who after some delicate questioning, clued them in on the circumstances of the world they'd ended up in.
"So which Archon is over your city?" Lumine asked.
The Outrider smiled, as she often did, her cheerful countenance leaking through.
"Lord Barbatos, the God of Freedom, is responsible for Mondstadt. Although, he hasn't been seen in quite some time…" Amber shifted her weight to one leg and put a finger to her chin, causing neuron activation in Lumine's brain.
(Hey Aether…)
[No.]
(What is it with you and having fun?)
[Lumine, these people may be mortals, but they have their own lives; we shouldn't sweep them off their feet just because we can…]
As soon as he finished the thought, Aether knew he'd made a mistake.
(Can't we? Since you're stuck with me, I can show you what you've been missing out on.)
Amber continued to smile sweetly at the Traveller, oblivious to her internal thoughts.
(Maybe I'll start a harem. For your sake…)
[You really are the worst at coming up with excuses.]
(Whaaat? You're the one always making excuses not to do anything with them! And you're the one who always end's up with the largest following, on every single one of our journeys!)
[That-That's-]
Aether struggled to come up with an excuse, causing Lumine to let out a soft giggle.
"Oh, are you thinking of something funny?" Amber asked, her eyes gleaming with innocence.
"Oh, something like that, hehe~" Lumine simpered, covering her mouth with one hand as she made the decision to conquer Teyvat.
[Lumine… Do we really have to?]
His twin responded by reaching out and gently taking Amber's hand, holding it in her own.
"Well Outrider, I'd be most appreciative if you could escort me to your city…" She asked with a shy look.
"O-of course!" Amber replied, shoving down the nervousness that had suddenly overtaken her.
"Great!" Lumine gave the girl's hand a slight squeeze, alongside her most charming smile.
"I'm looking forward to it."