In the end, the True Lung did not follow Sui's plan, for one very simple reason.
He could not bring himself to destroy everything he had built.
Back when he still bore the pure wrath of Sui, he sowed the seeds of suspicion among the commoners. He had intended to incite a new Hundred Clan Rebellion to shake the foundations of Yan, to use the flames of war to rend scars in the soil. Through this, he would obtain ultimate victory, becoming the king of a barren land, and the petty warlords beneath him would slaughter one another, and the people would know no rest. However, as he walked alongside the refugees across countless miles, he began to reexamine his mission. This was the first time he truly looked at humanity, rather than simply observing. As he looked up at the landscapes he once looked down upon, as he heard weeping and gratitude mixing together by his ears, he began to doubt himself.
If he truly was the entirety of Sui, he should feel only loathing and resentment towards humanity, so why was he trying to help them? Did he wish to obtain satisfaction from their fawning? Or perhaps... it was a sort of sympathy towards man and their morality?
But if he was not the bestial Sui Itself, then what was he?
A pair of eyes? A puppet?
If so, he should only be a tool for Sui's vengeance. From whence stemmed this... emotion?
He had no answer, only doubts.
These doubts grew and grew, and that first great fury eventually gave way to consideration for humanity. He revised his plans unceasingly, breaking apart the cruel scheme he had built with his own hands. In the end, the shadow of war became a shadow looming over the court, and when he realized his reason to 'seize the throne' was simply to hold the ultimate title of humanity, he was finally willing to admit—
Though his self may have originated from a Feranmut, he was no beast.
And so, Yan came to have a perfect True Lung.
He was involved in the writing of every decree, took interest in the appointment of bureaucrats, amended laws, formulated standards, and advanced the sciences. Under his talent and foresight, the people did not want for food or clothing, and enjoyed lives of peace. Catastrophes were predicted with precision, rarely ever causing major damage. Bandits were scoured from the nation, and threats from both the north and the sea were eliminated.
The Sui Regulator was granted even more authority, and their suppression of Sui grew even stricter. As for himself, he performed the rite of Feng Shan in the Garden of Grotesqueries time after time, peeling away the proxy body he so hated little by little, and through the rite, he cast it into the Tomb of Sui.
Now, he was undeniably human, and among humans, there were none as perfect as he.
As the True Lung, he had a mission, a duty: to lead his nation to the same realm of perfection as he.
So long as he existed, this temperament, this awareness, would not change.
...
The people of Yan have not seen their True Lung in a very long time.
It is not just the commoners. Even the mandarins of the Six Ministries have not seen hide nor hair of him.
One day, he suddenly expelled everyone from the palace, and ordered the Imperial Guard to seal it off. He has not shown himself since that day, a hundred years ago.
The lives of the populace remain as smooth as ever, and Yan does not suffer for her ruler's silence, continuing to be one of the few prosperous nations of Terra. Before the sealing, the True Lung had written a grand tome on all things big and small, thoroughly elaborating on every subject imaginable. Answers to almost every question could be found within: commoners consulted it to plan their lives, mandarins consulted it to understand their duties and responsibilities, artists and scientists consulted it for inspiration... The political system stabilized, the mechanisms dispensing rewards and punishments were flawless, and all did their duty loyally, without slackening. The True Lung had given them the answers to everything, after all.
Living life like this should have been incomparably wonderful... But everyone could sense a terrifying fact asserting itself: something had vanished from their lives.
...
The True Lung sits atop his throne, not a single pinprick of light by his side.
Why is it that humanity's greatest are always pushed towards sovereignty?
Is it to squander his talents, to force him to yield to the abyss of administration?
He has already done all a human can do, and recorded the entirety of it.
But to this day, there are still none qualified to stand by his side.
Mortals have their limits, and the True Lung was weary of doing such repetitive tasks over and over and over.
And so he wrote down the lives of all humanity, allowing Yan to prosper freely.
This was his final act of goodwill.
He does not regret becoming human. His self did not require the bestial Sui's control.
It is simply that even one as detached as he will always have things that cannot be resolved alone.
Yet mortals cannot keep up with him, and so, he sank into the irresolvable void.
Like a fowlbeast flying towards the sky, he can see the dark expanse of the heavens, and cast away the land behind him, but he will never be able to reach a single twinkling star.
Thus, he sits here, at a standstill.
...