It’s Wen Yuan who finds the crack.
It’s deep within the cave that Wei Wuxian has named the Demon Slaughtering Cave, hidden in a shadow and halfway behind a large rock. It really is the sort of thing a small, curious child is far more likely to find than an adult.
It’s Wei Wuxian who finds that while the crack itself is barely large enough for a somewhat thin adult to squeeze through, behind it there is far more space, as it opens into what appears to be a somewhat rough-hewn tunnel sloping downwards.
Well, technically Wen Yuan is the one to find it, except Wei Wuxian is the one to bring a light talisman along when he goes to fetch a crying A-Yuan who can’t find his way back and has sat down inside the tunnel.
Of course, once his Xian-gege is with him, Yuan is soon comforted and not at all inclined to go back. He wants to explore, and so does Wei Wuxian. Perhaps bringing a small child along is a choice Wen Qing will stab him with her needles for later, but - he’s got his flute and all the resentful energies of the Burial Mounds. What could go wrong?
So they walk together down the sloping tunnel, follow it as it meanders first to the right, then to the left, then right again, undulating their way deeper under the mountains.
At the end of the tunnel is a cave, and in that cave is an altar. The walls are covered in half-faded murals of fantastical things, that seem almost and yet not quite human - too large, too feral, too - wrong in sundry, subtle ways.
Wei Wuxian does not spare them much notice, though, because there are things on the altar - a bowl of rice and one of fruit as vividly coloured as gems and a single, burning incense stick.
If he’s any judge, it was probably lit - a very short while ago.
He tells Yuan to stand behind him, backs the both of them back to the tunnel they came from, and lifts Chenqing to his lips, but nothing stirs.
“Xian-gege,” Yuan whines, having gotten bored fast. “I’m hungry!”
The fruit is clearly a sacrifice to whichever ancestor or god this cave is dedicated to, but - well. Wei Wuxian bows to the altar and apologizes, putting two of his finest talismans on the altar and takes the bowl of fruit to share with Yuan. They settle down by the tunnel and lose track of time for a bit.
They smell it first - a musty smell, though not unpleasant. Then they hear it, a faint noise of something scratching, of small stones being disturbed by something’s passing.
Finally, they see it as it rises behind the altar.
At first Wei Wuxian thinks it’s just a snake. Perhaps a measuring snake, like those the Peacock had thought to impress his shijie with back on Phoenix Mountain. Some form of yao, anyway.
Then he sees the arms. The hands, thin, long fingers tipped with claws, holding a handful of unlit incense sticks.
The snake, in turn, sees him. Sees them.
For a moment all is frozen except the snake-person’s flickering purple tongue. Then - as Wei Wuxian watches, Yuan clinging to the back of his leg and breath ready to blow a tune - it puts down the incense sticks, lifts its arms and bows in polite greeting.
Wei Wuxian doesn’t argue. He did that days ago, when he and Yuan came out of the Demon Slaughtering Cave laden with baskets of fruits they could not name, bearing the news of their strange, but very polite neighbours.
The snake people have so far proven to be excellent neighbours indeed. They’ve brought gifts - cloth, farming tools, and of course food. Fruit, mushrooms, even dried meat - some form of pork, Wei Wuxian thinks.
They haven’t been to visit, though. The crack that connects their tunnel with the Demon Slaughtering Cave is too narrow for their serpentine bodies. But that’s alright. Wei Wuxian is happy to spend hours in the temple cave, listening as they tell their stories - of an ancient god, Ba-Hui, who sleeps deep beneath the mountain, about pilgrimages slithering through tunnels that a human would find all but impossible to journey through.
In sibilant voices, they tell him of a human kingdom long past, of sharing their alchemical secrets and their worship with people from the surface. Of having come together as something greater than their parts, and of how it ended, in blood and tears and flight deep, deep underground, as the neighbouring kingdoms took up arms and brought war and fire to their homes.
Wei Wuxian dreams of Lotus Pier that night, of the Cloud Recesses, of faceless armies of Wen cultivators.
And still, Wen Qing speaks against them, their kind neighbours. Several of the Uncles have gone into the caves to light incense in the temple cave and say prayers of thanks to the great Ba-Hui, and barely a day goes by without Yuan talking either Wei Wuxian or his uncle Wen Ning into letting him go below. He is endlessly fascinated by the snake people, and they in turn seem fascinated by him, letting him climb all over them as they carry on sibilant conversations, as they offer him more of those gem-like fruits and pinch his cheeks as he laughs.
Wei Wuxian almost gets a little jealous, sometimes.
But only almost.
“We do not have children, not like humans do,” they explain. “Our new brethren are fully formed upon their first shed, as Ba-Hui wills it.”
They offer to take him to Lanling along their paths, deep beneath the world, but he refuses. He walks in the sunlight with Wen Ning by his side and his world begins to fall apart.
If he could turn his head, he thinks he might see a grey-green arm trying to reach through the crack at the back of the cave.
He hears them scratching, claws against rock.
He doesn’t look back once as the third day comes and he runs out of the cave, barely takes the moments to reassure Yuan, safe in Granny’s care, that he’ll be back, before he leaves the Burial Mounds, far too late.
The snake person, the old priest with the scales gone greyer than any of the others, slides out of the crack, enlarged by sheer tenacity, large enough to let a snake person through.
It rises above where Wei Wuxian sits, ignoring his furious shouts at everything and nothing in favour of wrapping its arms around the scared Yuan.
Then it starts to sway, raising its voice in something a bit like a hiss and a bit like a song and perhaps most of all like the whistling of a flute, and Wei Wuxian finds himself grow calm.
“Come,” the snake person says and Wei Wuxian does, without a glance towards the cave opening and beyond, without pause for the sounds of ringing blades and screams that he cannot hear.
Once they are past the temple cave they carry him.
The tunnels are dark, and undulating. They’d be impossible to climb or crawl through, for a man, but the snake people move fast and sure, and Wei Wuxian and Wen Yuan are safe in their arms.
Far below the world they are taken.
The old priest sings to him as they travel, sings to him of the god Ba-Hui, of the rites of his priesthood, of the great gift. Sings the names of those who have been on this pilgrimage before him, and somewhere in the dark he hears the voices of his brothers-soon-to-be answer to the names.
Eventually they reach their destination and it is a cave of enormous proportions, strange crystals reflecting light to let him and see, and oh, he sees.
The snake is gigantic. The Xuanwu, horror that it had been, was like nothing compared to the snake.
Compared to Ba-Hui.
They carry him to the god and he watches as the jaws open, and somewhere he can hear Yuan crying. He’d like to turn around, like to reassure the boy that all is well, that this is right, but finds that he cannot.
The jaws shut around him, down here at the deepest part of the world...
... and he is reborn.
He knows there’s nothing to find. He knows that - others have searched, covered every inch of the Burial Mounds to find the hated Yiling Patriarch. He himself searched the caves and the area around the settlement, searched every nook and cranny, but found nothing.
No sign of Wei Ying and no sign of the child he’d left with him,
He does not expect today to be different.
He’s carrying two tablets, carefully carved in the finest wood. He’s carrying incense, and paper money, and jars of Emperor’s Smile.
He’s carrying a toy butterfly.
He’s making his bows, offering his prayers for the dead when he hears a noise behind him, like many stones sent tumbling, and he jumps to his feet, Bichen unsheathed as he turns to face - a snake.
Or perhaps not.
The thing emerging from an opening in the back of the Demon Slaughtering Cave, an opening that must have been covered by many rocks when last he was here, searching, is certainly akin to a snake, but also not, a pair of arms at its sides as it pushes itself upright, swaying slightly as if not entirely accustomed to the position.
It is naked, the snake thing, except a red ribbon wrapped tightly around its wrist.
There’s something thin and black cradled in its claws and Lan Wangji gasps at the sight, before letting his cold fury rise and Bichen with it. He does not care what this thing is, he does not care whence it came, all that matters is that it dares to be here and now and waving Chenqing around like some perverse trophy.
Except - except then the snake swallows its flickering purple tongue and hisses.