The thing about xiyao and truth serum is that I can't help but think more than anything they use it on themselves--to prove to the other that they're telling the truth, or to seek to know it. https://twitter.com/xiyaogarbage/status/1278120568827441152

There's a modern AU where LXC swallows nervously and downs some truth serum so that he can actually talk to JGY about what he wants, sexually speaking. There's another where they're alone together in JGY's rooms, and LXC looks at him calmly, and brings out the bottle,

showing it to him. JGY looks over it, frowning--it's clearly truth serum, why is LXC showing it to him? And LXC drinks it. And LXC starts in in what is clearly a prepared speech: how much he loves A-Yao, how much he admires how clever and competent and brilliant and socially

gifted he is, how beautiful he is, his much having A-Yao around has meant to him. It's prepared--but it has to be genuine: that's the point of the serum, JGY realizes, as he watches LXC, as he feels his heart start to crack, or possibly to mend. And LXC reaches into the same

pocket that held the serum, and brings out a ring.

Of course there's another universe where he stops JGY on the path, shows him the serum, swallows it back. Looking at the top of JGY's head he says, "I forgive you. And I'm sorry. But I can't," and walks away.

It would never have been practical, in the temple, but perhaps he imagined drinking some anyway, to tell LXC exactly how he felt, before he fled.

Perhaps there's a world where he wins after all in the end, quite comprehensively. Apologetically, regretfully, he takes

LXC prisoner--officially as a hostage, but that wasn't actually his main concern. LXC knows this because once a month JGY comes to his quarters and shows him the serum and drinks it, letting LXC ask him whatever questions he wills, before he gives LXC the same serum

and asks his own questions. It's always the same three:
have you told anyone else what I've told you, and will you?
Are you planning an escape, and do you know if anyone else is?
Do you still love me?

And then there's of course LXC in seclusion, post-canon. Once a week he mixes it and drinks, and discovers, grimly, what he still cannot say: I don't love A-Yao anymore, I wish I never had, the world is a better place without him in it.

There are other things he should try, but after the first attempt it's too painful to say out loud: if I could pick I'd bring A-Yao back before anyone else. I think he loved me more than anyone else ever has. If I could pick I'd have stayed in the temple with him.

He limits

himself, after that first attempt.

The funny thing is, too--during those sixteen years JGY would never take truth serum, deliberately, in front of anyone

(though he knows how it's prepared, another Lan secret his sworn brother gave him freely, another Lan secret

LXC will one day stare out into the room sightlessly thinking about, wondering how it was misused)

but, if he did--it would be LXC, he thinks. Who else after all would refuse to push him? Who else would take only and exactly the truth he offers?

But it would be an indulgence, and pointless. LXC could not give more credence to to his words with truth serum behind them than he already does without.

And then again, on the other end of the spectrum, a modern high school AU where LXC and JGY are playing a bit of a party game, truth or dare, traditionally played by stupid teenagers with a little bit of truth serum for added oomph

(and yes, of course JGY has swapped his out for coloured water)

and JGY asks who LXC wants to take to the prom

Not expecting at all LXC to say "You," and flush horribly

And of course you could use this for bedroom games in general, really. "Do you really want me to stop?" says JGY, gently, trailing his hand over LXC's stomach. "No," says LXC immediately, and ducks his head while JGY smiles.

@leatherbookmark once posited a world where JGY lives beyond the temple, and is forced to take truth serum at his trial--the problem being, of course, that being constrained to speak the truth doesn't mean he can't use his words as a weapon. I like that one very much.

Of course so far all this has been about injected truth serum, that makes you speak truly. What about a truth serum of another kind? A truth ink, say, that you cannot use to write false words?

*ingested, not injected

Maybe he writes letters to leave to Jin Ling, afterwards, defending himself--or maybe he doesn't. Do you think he could write "I had no choice," with this ink? Do you think he tries?

He does indulge himself in this universe, though, with the ink,

less of a risk by far than being bound to speak truly in LXC's presence, and uses it to write LXC love letters.

LXC thinks he understands it, at the time, that in Carp Tower surrounded by deception JGY wants to bind himself to visible truth.

After the temple he thinks about it again. His memory is not as exact as--his memory is not exact. He cannot recall every phrase JGY wrote to him, cannot remember which parts of what he read were implications and which stated openly.

It takes him a long time to gather the courage to go over them again, and see.