I made other posts about this idea, but I'm really starting to like the idea of Mu Qingfang and Zhuzhi-lang, so here's me gabbing about it a little more:
First, it's important to note I'm going off the back of one of my previous posts on Mu Qingfang. Basically I headcanon him as a deeply paranoid guy who joined the medicine peak not just to heal but also to learn poisons (because those are 2 sides of the same coin) because he views everyone stronger than him as a Threat and copes by coming up with ways to eliminate them Just In Case.
So somehow this version of Mu Qingfang runs into Zhuzhi-lang; perhaps Qian Cao originally had a different head disciple that died during the battle where they sealed Tianlang-Jun (or he simply wasn't in attendance), and disciple Mu Qingfang's first meeting with Zhuzhi-lang is in Bai Lu forest, on some kind of trip to Huan Hua. He's researching local flora and then runs into Zhuzhi-lang in his original form. He doesn't freak out or attack; after determining Zhuzhi-lang isn't hostile, he's fascinated by the possibility that he may have discovered a whole new creature. Since he thinks Zhuzhi-lang is just a monster/animal, he's less worried about him being a Threat like humans and demons are. If anything, he's curious if this snake-like being has any useful parts to use for medicines and poisons.
Zhuzhi-lang gains a fixation on this strange human and begins to follow and observe him. As the days pass, he's basically become Mu Qingfang's companion. He's more than happy to allow Mu Qingfang to study him (he practically preens when Mu Qingfang discovers Zhuzhi-lang is venomous, and eagerly harvests venom from him). Eventually, he leads Mu Qingfang to a cave, with glowing mushrooms blooming in the center of a lake...
Alternatively, disciple era Mu Qingfang (pre-sealing of Tianlang-Jun) gets sent to Huan Hua Palace with the other future peak lords on some kind of exchange program/bonding exercise. At some point a couple of Huan Hua disciples show them around the Bai Lu forest.
Mu Qingfang takes it upon himself to wander through the forest alone, looking for cool local plants after hours. Meanwhile, Tianxi is secretly meeting up and occasionally goes through the forest to do so. Zhuzhi-lang, after dropping off Su Xiyan at her window, is still in giant snake form when he stumbles upon a boy that seems to be digging through the dirt.
Mu Qingfang looks up to find two massive glowing snake eyes staring at him in the dark. He does not whip out his sword and attack; his background is such that his instinctive reaction is to freeze, observe, then (upon noting the serpent does not seem hostile) think of how to gain its favor. He offers it one of the blooms he dug up as a treat; its smell was known to be appealing to local reptiles, though it otherwise only had some mild pain-killing properties.
After slowly backing away, Mu Qingfang eventually returns to HHP, unaware that he's gained a new companion, who basically begins to stalk(?) him. Whenever he returns to the forest, he encounters Zhuzhi-lang in some capacity. His basic kindness and casual (trained) friendliness ensnares Zhuzhi-lang, who famously doesn't understand how human politeness works, and soon he's leaving gifts of all sorts in Mu Qingfang's room whenever he has the opportunity. Tianlang-Jun does everything BUT help the situation, as he gets immense joy from watching his nephew go ga-ga over some cultivator boy ("it runs in the family," he crows) and gives him terrible advice from his books.
To avoid this post becoming too long; Mu Qingfang will eventually discover Zhuzhi-lang is not just a demon, but a heavenly demon. He becomes very fascinated upon researching all the things a heavenly demon is known to be capable of, medically speaking. Such a resilient specimen, resistant to all known poisons, insane regeneration rates... this is the closest to hot and bothered Mu Qingfang has ever gotten. Perhaps especially if the timeline follows canon and Luo Binghe is revealed to have both (heavenly) demonic and human spiritual energy, before committing all that fuckshit (kidnapping MQF for 5 years to preserve his teacher's corpse and then almost ending the world til he finally got his dick wet), he may become especially motivated to discover just how invincible heavenly demons truly are...
Of course, poison, like medicine, must be tested to be proven effective. But if the target is a heavenly demon, then the subject must be as well...
Zhuzhi-lang is, of course, all too eager to volunteer himself and his body for all of Mu Qingfang's needs.
