Before Song Qingshi falls into a coma for ten years

There's a timeskip where Yue Wuhuan has a decade to live outside Song Qingshi's observation. Instead of letting his "new self" show through his actions, we're directly told who he is via narration.

he would be willing to die if only to make others feel better and has no regrets. If An Long wanted him to die, he could die at any time. He is deeply insecure and displays suicidal tendencies.

• Millions of years ago, the celestial gods in the heavens presided over the World Tree, a tree upon which each fruit was a “small world” with its own universe. The gods were constantly fighting off the demons, who sought to corrupt these worlds and use the negative power created by corrupted worlds to defeat the gods.
• Yue Wuhuan is the phoenix god and his domain is cultivating these worlds on the tree and helping them avoid collapse so that one day they may become stable and self-sufficient without help from the gods. He created a “system” to automate this process by way of designating a “tasker” to help guide the world’s progress.
• One day, the entrance to the Underworld appeared and was leaking evil energy and Underworld Fire into one of these worlds, trying to corrupt it. The celestial emperor stopped up the leak by forging a normal rock into a beautiful stone and using it as a plug. Over time, humans and cultivators worshipped this stone and it accumulated positive merits and eventually cultivated to ascension. It took human form and became Song Qingshi. Yep. That’s why he’s literally as blank, unfeeling, and oblivious as a rock in the beginning.
• YW noticed the emperor setting down this beautiful stone and, as it’s his hobby to collect stones and gems, he wanted it; he had never seen a stone as beautiful and eye-catching as this. He was at first depressed to learn that it “grew legs” and cultivated to human form after stopping the Underworld leak, and decided to “collect” this beauty once it grew a heart and could love him back.
• SQ didn’t understand emotions or the ways of the other gods, so the emperor sent him to study in a private palace in the mountains. All day, for thousands and thousands of years, he studied and read and tried to understand; his only respite from this single-minded determination to know was the beautiful phoenix that liked to show off every day. It was the only color in his life, though he and the phoenix never met.
• The demons, in their ever-persistent scheming against the celestial gods, decided on a new tactic to corrupt the worlds and thereby create more negative power for themselves to absorb. They “hacked” YW’s system, making it so that those who enter the world would have their memories wiped and be punished if they didn’t follow the plot, and stole a piece of soul from YW, then crafted an avatar in one of the worlds for him to exist in. Though everyone else thought the Phoenix was perfect, in fact, he had severe flaws: he was proud, mysophobic, unyielding, and obsessive. The demons used these flaws to design a custom hell for him, one in which he was fated to be defiled and betrayed unceasingly, never to find happiness. With his nature, he would generate hatred towards himself, others, and the world itself, and this hatred would be an infinite generator of negative power for the demons.
• YW fell into the demons’ trap and forgot his true identity, experiencing thousands of incarnations of suffering. Meanwhile in the heavens, the World Tree and all its other worlds was slowly becoming corrupted without his influence. But because the system was hacked, the gods could only interfere and rescue him from within–they would have to become “taskers” and fight against the demons’ system to wake him up.
• The demons used the gods’ weaknesses against them; all who entered became distracted by the pleasures the system could arrange for them in this world or became pawns of destruction used to antagonize YW. An Long (AL) was a friend of the Phoenix and a general in the heavens, but in trying to save YW he became tortured by his inner demons and his relationship with YW was twisted to the point where they were rivals and enemies in this world. He too was lost to the system.
• SQ noticed that the phoenix hadn’t flown by his mountain in a while and, after learning that it was YW who was in a coma and whose piece of soul was being endlessly tortured in one of the small worlds, determinedly became a tasker to save the only piece of color in his blank existence.
• YEAR 1 (I’m assigning this a number for the purposes of tracking the timeline) SQ’s first incarnation as a tasker was to save another character named Qu Yurong from a miserable fate, but upon seeing the poor YW, something in his was drawn to the boy and he mistakenly saved YW. Unfortunately in this incarnation, YW was blind and illiterate, and SQ–as a still-relatively-young former-rock–was mute. Still, through his authentic earnestness and transparently-innocent motives, SQ managed to gain the trust of YW–something no other tasker or god could do. While others got tangled up in their own happiness or hatred, SQ was uniquely dedicated solely to YW and the seed of obsession was planted.
• Gradually, SQ learned about emotions and human experience from YW and YW learned to lessen his own self-loathing because SQ loved him. They eventually became Daoist Companions and YW, driven by his desire to get stronger for SQ, started cultivating the Way of the Sword, eventually taking the name Mo Yuan (MY).
• It was good for many centuries–YW/MY was protecting people because he knew SQ didn’t want to see people hurt, and SQ practiced medicine and became an infamous doctor. Then fatefully, SQ found the original “protagonist” he was tasked to save, but Qu Yurong was too far gone and eventually killed himself. The system deemed SQ’s task a failure and punished him, causing him to have harmless but demonic markings on his body at the same time as a demonic plague was occurring that YW was fighting. The people believed SQ to be the culprit of the plague and tried to kill him while YW was away. When YW returned to his Daoist Companion, SQ died in his arms and he went mad, destroying everyone then being killed.
• Before dying, YW caught a glimpse of the truth of this world and its system. It was too late for the MY incarnation of himself, so he created a trap formation that would prove this truth to his future incarnation. This formation would be activated 8000 years in the future.
• I believe this is also around the same time that, while in limbo after dying in YW’s arms, SQ separates a small part of his soul to go to the modern world to “gain experience” while his main soul stays in the cultivation world for the next reincarnation with YW. The text in chapter 77 says, “Song Qingshi chose the world of immortal cultivation where the Phoenix’s power was strongest, and put down a lot of clues. He then cut out his heart and a part of his soul and threw these parts of himself into a simple small world to gain experience. He placed his body into the immortal realm to concentrate on cultivation and become the perfect vessel.” Prior to this separation in the first incarnation, SQ clearly learns to love. In the next reincarnation after the separation of heart and soul, SQ is heartless and unfeeling and completely focused on honing his medicine skills.
• YEAR 7000 SQ reincarnates as the future Medicine King, he’s still stiff and doesn’t really know how to interact with people (because you can infer that he’s missing his heart, which was sent off to the modern world). Presumably, he has the same task to save so-and-so, though we know once his soul catches wind of YW he will want to save him.
• YEAR 7200 SQ saves a half-demon child from death, not knowing that the child is An Long who imprints obsessively on him
• YEAR 7500 SQ meets AL “by coincidence” (the system using AL’s weaknesses to make his love for SQ futile while also using AL to antagonize YW)
• YEAR 8000 SQ is killed by AL who momentarily is compelled by demonic influence to lash out when SQ refuses to return AL’s feelings. Horrified by what he’s done, AL flees and SQ’s other vessel in the modern world dies at the same time, resulting in SQ coming back to life and “waking up” and believing himself to be a modern man who has transmigrated to the cultivation world. His system task is to “save the protagonist shou”. This is where the book actually begins.
• SQ finds YW as a teenage s*ave in Jin Feiren’s courtyard and is immediately entranced. Believing the boy to be the so-called protagonist shou, he is determined to save him. He rescues YW and brings him to the Medicine King Valley to rehabilitate and study, and along the way they run into AL who’s unaware of SQ’s amnesia and the 3 of them (plus the sweetie pie white snake Xiao Bai) have lighthearted adventures while SQ slowly heals YW and learns more about himself and his developing feelings.
• SQ frees YW from his s*ave mark and the two cultivate feelings towards one another. SQ feels that his current Dao Way, the Way of the Heartless, is crumbling due to his emotions towards YW. In his damaged condition, he successfully helps YW ward off the system’s abnormal lightning strike tribulation when YW reaches Foundation Building cultivation level, but SQ is left in a coma. YW is spurred to study like mad and travel to the ends of the cultivation realm to heal and revive SQ.
• YEAR 8010 YW wakes SQ up from his coma and SQ’s soul is finally complete; the heart and piece of soul that he cut out and sent to the modern world which returned to him after AL killed him has finally become whole and his memories slowly come back. He is able to act on his feelings for YW and the two eventually decide to become Daoist Companions, with SQ as usual giving his all to result in YW’s happiness.
• When AL spies the two kissing, his demonic side comes out and the system takes further control over him. YW discovers AL’s secret and like the yandere he is–like the system has arranged for it to be–he feeds AL’s toxic obsession while displaying his own deranged need to possess SQ.
• AL disappears and the happy couple gets closer, though SQ has recognized that he will need to change his Dao Way since the Way of the Heartless is cracking under his love for YW. YW would rather die than let SQ experience the pain of his cultivation breaking, so SQ secretly makes preparations to face the system and hand off his cultivation power to YW before it’s completely destroyed.
• SQ knows the system is using AL as a pawn and goes to face off AL. AL ends up going berserk and the two stab each other; SQ is killed and his soul is whisked off by the system and AL sees himself forcibly revived. Because SQ failed, another tasker is sent to deal with YW and tells YW that his fiancee is dead. YW awakens his hatred and tries to kill himself on Inextinguishable Peak but the system’s twisted hand of fate keeps his soul alive by saving him so that his misery can never end.
• In limbo, SQ sees that the system is in the process of breaking down; golden merit power appears to be wearing it down, causing the errors in bestowing and managing the tasks. He realizes the truth of the solution: only with this most pure and benevolent Golden Light of Merit can the system be defeated and YW can be truly rescued. This is why he has always subconsciously been helping people via medicine and why he even started a school to pass on his life-saving knowledge. Over time and with the butterfly effect, these little actions lead to a massive accumulation of merits, and he’s going to need a ton of them to break the system and save YW.
• YEAR 11000 It’s been 3000 years and SQ wakes up in another reincarnation with again no memory except that he’s looking for someone; the system is almost completely broken and his task is just “eliminate this world’s villain”. He’s found by a great-great grandson of YW’s assistant and brought to the now-prosperous Medicine King Valley sect. YW is the most powerful immortal in the world and has multiple avatars, but he wants to leave the old, dirty him in the past, so when he senses SQ’s awakening he makes every effort to disguise himself and their past together while getting closer to SQ.
• The pair inevitably rekindle their feelings even though SQ has only a faint inkling that he’s met YW before and that YW is special. The two of them (plus the now-giant sweetie cutie pie baby white snake) go on an adventure to save the grandson’s best friend, who incidentally is now the system’s protagonist and “right answer”. In their adventures, they stumble upon YW/MY’s formation, the one that he made after the first SQ incarnation died and he glimpsed the truth for his future self.
• The formation allowed YW and SQ to relive their first life together, when SQ was mute and YW became Mo Yuan. After dying in the formation, SQ was issued an option from the system to “restart” and immediately chose to relive the previous incarnation. He found after hundreds of tries that the task was a Catch 22–an impossible problem–and that either A) he would save Qu Yurong and YW, with his obsessive nature, would sabotage the saving, causing SQ to fail and die again or B) he would save YW as he always was want to do, but Qu Yurong would die as a result of not being saved from his miserable fate. Still, SQ chose to try to do the impossible and save both every single time. And in every lifetime, he loved YW. He realized that his task to “find the right answer” (save Qu Yurong) was truly unsolvable, and was resolute in pursuing the “wrong answer” (YW’s happiness) without ever giving up.
• YW was able to see SQ choosing him over and over in the formation and his insecurities surrounding being the “wrong answer” and his obsession with needing to eliminate all other “answers” were assuaged. Although SQ had managed to heal him partway with his authentic nature and genuine trust in YW, YW had to heal himself the rest of the way by leaving a formation for himself that would allow him to truly and deeply acknowledge SQ’s dedication and love and accept it as truth.
• The two of them realize that the system can only function with YW’s hatred, though a large part of its power comes from AL who has escaped in the midst of a demon plague uprising. The system is losing its grasp on the world and fierce demons and malevolent energy are sweeping the world. As it power weakens, SQ’s previously-wiped memories flood back and he’s enlightened.
• The only way to destroy the system and wake up YW was through the most benevolent and pure power against the demons: golden merit. SQ was able to lay down clues and subconsciously work towards this solution of farming merits in each incarnation. The huge amount of merit he gained from saving lives as a doctor and spreading his knowledge of medicine to future doctors was able to invade the system and cause errors and weaknesses in it, slightly sabotaging it each time. Finally, in this incarnation, he is able to get YW to free AL from the system’s demonic influence with a sword crafted of Golden Light of Merit. It contained all the millions of merits obtained directly and through the butterfly effect of SQ’s actions, and was enough to defeat AL and reveal his true celestial form, after which he returned to the heavens.
• The world was rid of the plague but YW was still not free; the system would always have its hold on him if he didn’t heal this one last part of his heart demons: hatred. Leaning into the perspective of his beloved SQ–and in the light of almost killing SQ with the black hatred that spewed from him as he fought AL–he extinguished the soul lamps that he had been keeping and torturing for 3000 years, and with each one he let go, a shackle was released from his heart, and his beauty mark disappeared. At last, the seal containing him in this filthy world was broken and the two awoke in their true celestial selves.
• The gods who escaped the system such as AL sealed their memories, and when the Phoenix awoke from his coma–his soul now intact after millennia of torture at the hands of the demons–SQ expected that the popular and charismatic YW would want to seal his memories too. After experiencing so many things in the thousands of years with YW and by himself, SQ was no longer stony and heartless and he felt desperately lonely where before he felt indifferent. He cried and tried his best to accept YW’s decision but was surprised to find YW at his door, having chosen to hold onto all the memories–the good, bad, filthy, and ~dirty~ ;)
• YW rerouted the small world’s trajectory so that the friends they made in it could live normally. The two of them restored their Daoist Companion bond and got married. The extras gave a happy ending for the original “shou protagonist” Bai Zihao and he got his own peac*ck yao god husband. YW’s beauty mark canonically comes back every time he gets pent up and SQ uses it as a timer for when it’s time to stop studying and go assist his husband. They adopt Xiao Bai and the snake cultivates to human form, eventually becoming a very s*upid but loveable soldier. All the couples apparently use the small worlds for sexy roleplay times, and apparently the beastman world where SQ gets bunny ears and a bunny tail is a favorite. Truly, this is a Happy Ending.
  
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I also despise love triangles a lot. I can read novels where the best friend has feelings for the MC. But only if the MC was making it clear to the best friend that it wasn't reciprocated. The MC in this novel was very dense in terms of understanding feelings.

For this to extend to godhood and celestial talk, I'm quite impressed that the author made generally unrelatable beings, relatable. Though, towards the end, it muddled the sterile purity trope through. The 'defiled' body wasn't real but the memory was. The ML accepted that dark and dirty past and moves on.

Not saying I wish he was better of remaining partially broken with that physical and emotional trauma, but it lost a bit of the genuine hurt that build his character, if you know what I mean. Given, the ML uses also that experience later on as growth, it doesn't change the fact the author tried to clean wash his physical being and put it aside and a terrible nightmare or simulation.

After all, their love relationship developed in this 'simulation' and it's not like the woke up and walked separate ways....I suppose that's my sole complaint, as well as conflict.

What I loved about the novel was how deeply the transmigration system plot got. It was thoroughly explored and even got exposed to the ML.

Gotta admit I'm fed up with protagonists hiding the truth of their background from their lovers (especially those who trade the target's sincerity for system points, that's to me, exploitation; not that the MC does it since ML is the wrong target as depicted in the synopsis). Not many are this upfront about their transmigration and reason around their said-target. This misunderstanding helped further strengthen the couple's bonds.

The true villains:

The true nature of demons has been briefed to us but the whole idea of an entire race being inherently evil here is rather subjective.

It was the celestial beings that were more powerful and oppressive, sealing the demons away. They made the gods face their own desires and evil, meaning the gods were also flawed in a sense.

This is another aspect which makes this psychological novel great, making perfect beings face their own imperfections and not simply set two camps and have those two fight it out. I really would've loved to see more about the demonic races, having just finished 'Devil Venerable Also Wants to Know' and it's concept of equilibrium.