oooh wait. what if Flare-Up!Shen Yuan is like a superpowered evil side in its advanced stages? (i'm picturing something akin to Inuyasha going Full Demon Mode and losing himself in demonic instinct)
Like there's stages to a flare up:
first Shen Yuan gets snippy and easily irritable, left untreated he progresses into the second stage of being outright verbally belligerent to anyone and everyone (it's at this point that his flowers and eyes start to turn red), third is when he starts getting physically aggressive (flowers and eyes are fully red at this point) (the first time Shen Yuan hits one of his sprouts. like actually hits with real force, he has a breakdown after getting snapped out of it), and the fourth stage is where Shen Yuan is driven on a murderous rampage, the poison encouraging him to spread it further and infect every living thing he can reach (a bit like that parasitic fungi that puppets the bodies of wasps and ants).
Snapping him out of stage one is relatively easy. A qi infusion helps reset his internal balance. Tears often break him out of stage two, but not always (the Bai Zhan disciples quickly learn the Bingmei Tactic of manipulating Shimu by bursting into tears at the drop of a hat). Stage three, he has to be physically shaken from by a strong cultivator (this is because breaking Shen Yuan from this stage almost always ends in a fight and only someone like Liu Qingge can do so safely. He wouldn't let anyone else face his wife anyway. Not when he's like this).
They've never had to figure out how to deal with stage four. It's largely a hypothetical based on the logical progression of the first three stages and the effect Without A Cure has on Shen Yuan's qi and flowers.
When the Old Palace Master makes the moronic move to kidnap Shen Yuan, the stress of the situation propels Shen Yuan into a flare up ("because of course it does!" Shen Yuan curses) that he can feel is going to spiral wildly out of control. By the time he finally poisons the Old Palace Master, Shen Yuan is holding onto himself by his fingernails, but while the Old Palace Master is choking to death on his own blood, he's thrown into a violent qi deviation and attacks the nearest person. That person being Shen Yuan (and this is intentional on the Old Palace Master's part. Or as intentional as it can be with the state he's in. But even fatally qi deviating as he is, the Old Palace Master violently hates Shen Yuan and even if the Old Palace Master dies, he's taking Shen Yuan with him). His tenuous hold on his presence of mind finally slips.
When Liu Qingge finally arrives at Huan Hua palace, it's choked by violently red flowers that seem to glow with malice, all growing on woody vines covered in wicked hooked thorns that glint with poison. Huan Hua's cultivators and disciples are desperately trying to escape the poisoned vines (especially when the first few die violent deaths just from getting pricked by a thorn) but find their exits blocked at every turn, the palace turning into an ever shifting labyrinth of deadly vines and flowers. It gets worse when the flowers seem to start hunting and even formerly innocuous plants that grew around the palace start to change (because that's what Without A Cure does to any plant it infects. It tries to spread itself as far as possible by any means available).
It's all very Thorn Forest from Sleeping Beauty if the thorns were sentient, covered in deadly poison, and actively trying to grab you.
Luckily for Liu Qingge, he came prepared and at this point is well versed in facing Shen Yuan in this state. Though, he'll admit, it's way worse this time.
Liu Qingge finds Shen Yuan in a garden at the center of Huan Hua's complex. The whole garden is choked with vines of violently red plum blossoms that burrow through the ground, the stone walls, and climb up the open skylight like a desperate swarm. In the center of it all is Shen Yuan, eyes redder than Liu Qingge has ever seen them, blood red plum blossoms spilling down his shoulders. He just stands there.
At his feet, the Old Palace Master's body is being rapidly consumed by the nearby plant life, the skin and flesh stripped from the bones as its gradually pulled underground, the only indication of who that corpse used to be being the fine gold silk robes it wore that are now being slowly shredded.
No. Liu Qingge takes it back. Shen Yuan isn't just standing there. He's rooting.
Right before his eyes, Shen Yuan is becoming a tree. It's something that nature spirits like Shen Yuan can do in times of crisis to recover their energies if they find themselves far from their bonded tree. Or if there is no bonded tree, they can become it themselves.
I just like the idea that Liu Qingge has to reach Shen Yuan not just physically but mentally as Without A Cure functionally encourages him to abandon his human form to root and establish a foothold for Without A Cure to continue spreading like a plague. "I know you're in there somewhere" scenes are a guilty pleasure of mine.
For extra angst, Liu Qingge's defenses are breached by the advancing vines and he gets infected with Without a Cure before he fully breaks Shen Yuan out of the trance. Worse, the rooting process is too far along for Shen Yuan to stop even without the flare up encouraging him to do so. Just. Shen Yuan holding Liu Qingge as his limbs turn wooden and branches sprout from his back and shoulders, desperately pouring whatever healing qi he can pull from within his already exhausted reserves to forcefully keep his husband's meridians from collapsing, fighting against the ingrained instincts of his kind to slip into the rejuvenating slumber that rooting will provide because Shen Yuan knows that if he stops now Liu Qingge will die in minutes.
But he can't hold onto his consciousness forever. Eventually, even as he fights tooth and nail to hold on until help--if it's coming at all--can arrive, Shen Yuan's reserves finally bottom out and he succumbs to his rooting.
Luckily for Liu Qingge, Mu Qingfang arrives not long after. Shen Yuan successfully bought Liu Qingge the time he needed for help to arrive (because of course immediately after Liu Qingge rocketed off to go save Shen Yuan, the others followed. They were only this late because Liu Qingge is a very fast flyer especially when he's motivated). I also think that Shen Yuan would absolutely have worked with Mu Qingfang beforehand to formulate treatments for Without a Cure just in case the worst came to pass (because Shen Yuan is trope savvy enough to recognize a Chekov's Gun for what it is, especially one so obvious). As Mu Qingfang works to stabilize Liu Qingge, he bemoans that such measures have to be put to use on the one Shen Yuan least wanted to hurt.
Liu Qingge returns to Cang Qiong for some heavily enforced bed rest until they get Without A Cure thoroughly under control. But of course, Liu Qingge is antsy. The cause this time is one that every one of his martial siblings can sympathize with because every time Liu Qingge slips away from the mountain against medical advice, he isn't found in some far off wilderness testing his strength against a ferocious beast. No. Every time, they find Liu Qingge in the center of what used to be Huan Hua Palace, sitting at the foot of his wife's tree.
After the Day of Bloody Flowers (the day Shen Yuan fully succumbed to Without A Cure), Huan Hua Palace has been abandoned. The Old Palace Master is dead, as are a fair number of its hall masters and senior cultivators. Anyone who had been close to the garden when Shen Yuan lost control was dead before they even realized they should panic. Nearly all of them had been part of the Old Palace Master's inner circle and the upper echelon of Huan Hua's power structure (all of them had been waiting in anticipation for the Old Palace Master to share the spoils of his latest acquisition. In a way, they got what they wished for). Thankfully most of the disciples made it out with only mental trauma but after that day, Huan Hua was functionally no more.
And no one dared approach the place either, even after Cang Qiong worked tirelessly to quarantine the grounds and carefully crush any blade of grass infected by Without A Cure, save for the plum tree at the epicenter of this whole mess. That, no one dared to touch. Especially not with the War God of Bai Zhan standing guard over it more often than not. Poisoned he may be, but he is still a formidable opponent and more than happy to prove it to any who might threaten his beloved.
Eventually Mu Qingfang and the other Peak Lords stop trying to keep Liu Qingge from Shen Yuan's tree, and instead go to him to help manage Without A Cure. It's a miserable poison to suffer, even for a physical cultivator like Liu Qingge. Perhaps especially so. The knowledge that his strength has been functionally hamstringed is a devastating blow to his pride matched only by the painful silence hanging over his house like a funeral shroud. He can't bear to linger in that empty house when the echoes of Shen Yuan's presence ring around him.
So he stays at Shen Yuan's tree. He culls any corrupted sprouts that spring up in the slowly healing soil (after all, what's the worst that can happen? He gets more poisoned? Mu Qingfang will chew him out for this later, but whatever). He feeds qi into the plum tree that was his wife, feeding along side it the fragile hope that someday Shen Yuan will recultivate his human form.
That day comes five years later (because of course it does).
Liu Qingge is meditating at the base of the plum tree as usual, seeking shelter from the rain that pours in through the skylight and solace against the smooth trunk (the trunk, to outside perspective, is oddly shaped with a wide protrusion that looks like it could cradle a grown man. Liu Qingge leans against that part often), when a crack like thunder rings out directly next to him. There's a massive fissure splitting the tree and it glows from within with a radiant light. At first Liu Qingge fears that the tree was struck by lightning before he realizes he knows this light.
The tree continues to split open, wider and wider, until at last, a person stumbles out, all pale jade skin and inky black hair. Liu Qingge knows this person--this man, for all that he still looks more feminine than masculine. He knows him like he knows the shape of Cheng Luan's hilt in his hand.
Shen Yuan loses his footing almost immediately on the uneven terrain at the foot of his new tree, but Liu Qingge is there to catch him as he was there the first time Shen Yuan gained legs in this life.
Their reunion is full of frantic, joyful tears that are quickly lost in the falling rain. It's only when Shen Yuan shivers in the chill of the rainy evening that both of them remember that Shen Yuan doesn't have any clothes on (Shen Yuan doesn't mourn the gaudy gilded thing the Old Palace Master and his cronies forced on him when he was first brought to Huan Hua, but come on! what's with this lewd wife plot nonsense! he may technically be a wife but using the same thing twice is ridiculous!). Liu Qingge, face red as the poisoned blossoms that once grew uncontrollably from his wife, wraps Shen Yuan in his outer robe and ushers them both into one of the chambers that remained intact after the Day of Bloody Flowers and all that came after it. It's a decrepit room now but Liu Qingge had claimed it for his own and made it as much of a home as it can be without anyone to share it with.
They sit together on a velvet couch that has lost all of its legs and half its backrest, dripping wet but together and alive.
Then Shen Yuan twists to grab at Liu Qingge's face, frantically asking about Without A Cure and his husband's health. He's relieved to hear that in the time Shen Yuan was asleep (five years! he can't believe it), Mu Qingfang has kept his martial brother in good health considering the circumstances. Though as Shen Yuan looks at him more, he notices the ways Without A Cure has weighed on Liu Qingge. He's colder than Shen Yuan remembers, and not just because of the rain, his skin waxy and pale in a way that is unhealthy, he's grown lean in ways that his cultivation wouldn't have allowed before even if he hadn't trained with as much focus and dedication as he had before his core had formed.
Liu Qingge assures Shen Yuan that it's alright. He's alive. He can still cultivate, albeit at a slower rate than he would have preferred. It was worth it, the poisoning, the five years, all of it, just so he could see Shen Yuan again.
Shen Yuan, however, finds this situation unacceptable.
But fortunately, he may have a solution.
During the five years he spent as a tree, Shen Yuan had focused on that dreadful poison within him and set about turning its own nature against it as it had tried to do with Shen Yuan. The result is what Shen Yuan hopes will be a cure for the thought-to-be incurable, a poison that roots out and destroys other poisons.
The Without A Cure within Shen Yuan has become an Every Cure. A panacea.
One problem though: Shen Yuan doesn't really know how to use it yet. But there is one method he's quite certain will work given the world they live in.
(it does work. Naturally)
