They are going to change Xing. Ling/Lan Fan, spoilers to manga chapter 49.
notes: I take a lot of liberties with Xing based on what little backstory we've gotten for Ling and Lan Fan. This is a few years post-series, assuming that the first place Ling and company went after leaving Xing was Amestris. It also takes some liberties with how the series might end, although it's very vague there. Also, I'm using the fandom convention of translating 'rentanjutsu' as 'pharmacy' in lieu of having an official translation (since lord knows it will take ten years for them to get to volume eight).
Xing rots away from the inside, sealed in its own corruption by the desert and the sea that separate it from other nations on either side. Ling has known it for years, nearly as long as he can remember, the intrigues and clan wars and succession battles a blight on them all underneath the colorful silks and affected manners of the imperial court.
Ling Yao is the twelfth son of the Emperor of Xing, too young to be considered a real threat in the struggle amongst his older brothers but not young enough to be ignored entirely, especially since his Yao mother has taken his education upon herself and the clan members that have accompanied her to the capital rather than leaving him to be tutored in the court. Yao Ling has also been missing from the empire for three years and has been all but forgotten by the brothers who plot against one another, presumed to be dead or to have abdicated his position.
Ling hasn't forgotten about them. He also hasn't forgotten the reason he needs to supplant all of them, so that he can finally cut out the rot at Xing's core and let the nation grow again. He is not content to ignore the problem as his ancestors have, covering the stench of decay with perfume and incense. Even if he's abandoned the idea of finding immortality through Amestrian alchemy, he hasn't changed his plans to push his homeland onto a better path. Not with as many sacrifices as they all have made for it.
"Are you ready, young master?" Lan Fan asks quietly from where she sits near the window. They're in a western-styled building on the outskirts of the imperial capital, an inn for foreigners run by a fair-haired man who seems surprised when a pair of Xingians want a room there and even more surprised when the man asks for it in perfect Amestrian.
She had been the one to choose the inn. /Foreigners are less likely to know who you are or what my mask means, young master/, she'd advised him, and he'd listened to her. The atmosphere here is tense, because the stories of Amestris' carefully-placed strikes at neighboring countries (Ishbal, Lior, Drachma) has reached them even across the desert. Somehow, the stories of the military coup and ensuing peace that's been in place for two years haven't done the same, and the imperial capital of Xing is not a comfortable place to be Amestrian now.
He realizes, sickeningly, that she started calling him young master again as soon as they approached the borders of Xing, at the end of the desert.
"Lan Fan." Ling places his hand on her shoulder- her intact shoulder, not the one that was long ago lost and replaced by automail- from behind. She has suffered and changed enough for Ling's plans and for Xing that she can't succumb to the poison in their country. Not now. "You haven't called me young master in two years, since we were in Amestris."
"But we aren't in Amestris anymore, and there are things that must be observed when we are here." Lan Fan doesn't turn around; Ling is the only person she allows to come up behind her like that.
"Not here," Ling says, his voice strained and strange. "In court, maybe, or around the Yao clan. But not here, never here."
"Not here," she agrees finally, laying cool metal fingers on top of Ling's. They're the most enduring sign of the change in Xing that will start with them; had she lost her arm in Xing, a talented royal pharmacist might have been able to save it- would likely have been able to save it. But they had been in Amestris, where alchemy was used only to destroy and kill, and so she had an automail replacement the likes of which was rarely seen in Xing (and then only among the few foreigners there).
Xing will open up, because closed wounds only fester.
Lan Fan is holding her mask in her lap, worrying at the ties with her free hand; she hasn't worn it since they entered Xing proper, no matter how much she would like to retreat behind it. Ling needs to remain anonymous until he's ready to reveal himself, and the design on her mask will tell anyone noble enough to know that she is bodyguard to a member of the Yao clan.
"Besides," she continues, quieter still, "It won't be appropriate to call the Emperor my young master."
"I'm not the Emperor yet," he points out, sliding his hand up her fingers and over the steel-alloy wrist joint until it rests on her cool elbow. When they'd fought together, Edward Elric's automail arm had always seemed warm as anyone else's flesh arm, but Lan Fan's metal arm doesn't seem to retain body heat the same way. It's nearly always cool to the touch. "And even when I am, I hope you'd still call me be name when we're alone."
Even with changes in Xing, Lan Fan will never be his wife. Having wives from clans that the imperial throne needs to ally with or keep in line will probably always be necessary. But she's something far more important- his sworn bodyguard since childhood, the only person he'll ever be permitted to be completely alone with once he's crowned Emperor.
Lan Fan stands up then and turns to face him, laying her mask down on the chair she's been occupying.
"Ling," she says, using his name for the first time since entering the borders of their homeland, "If anyone can change Xing, you can."
She never doubts him. And it's not only her oath to his clan, the blood-sealed bond that would keep her as his unwavering support even if she'd hated him; she's seen him do so many impossible things that doubting him seems foolish. He's killed what couldn't be killed, survived what should have killed anyone else, and is the one who will change what can't be changed.
"Not without you." And it's spoken with such simplicity that it's not maudlin or sentimental. Ling merely states the truth; without his bodyguard (companion, friend, lover) he would not have been able to do any of the things they both remember.
"My life is yours to do with as you see fit." It is an echo of the oath sworn by members of her clan to the Yao, spoken as he slides his hands up to rest on the bandages binding down her breasts.
He desperately hopes that he can use it as well as she deserves.