Wan Zhong Daoming was the leader of the Fenghua Sect, known as the Venerable Wan Zhong. In his entire life, he took only one disciple. The greatest Venerable in the world, and the only one ever to reach the Deification Stage, he endured the Tribulation of Deification for nine whole years, until at last... he was struck dead by lightning.
...This is ridiculous!
By all rights, his soul should have been scattered to the winds. Instead, he ran into some busted thing calling itself the Deification Evaluation System. The System was sobbing uncontrollably. Ever since Wan Zhong Daoming had died and fallen from the path, his sole, beloved disciple had entered the demonic path, slaughtered the world, and plunged it into endless chaos.
Millions of cultivators across the three realms, driven to the brink by the harassment, submitted a blood-written petition demanding that this damn thing be killed. Ahem, no, demanding that Si Mo, the scourge bent on destroying the world, be eliminated!
System: Please find a way to eliminate the Demon Venerable Si Mo, and I will reward you with a grand ascension gift package!
Wan Zhong Daoming, fiercely protective of his own: Hah.
System: ...I can sweeten the deal!
Wan Zhong Daoming: Get lost.
Just when Wan Zhong Daoming thought things couldn't get any more ridiculous, Si Mo, clad in crimson, crossed the Milky Way, tore through space, and appeared before him. His eyes bloodshot, he gazed at the resurrected Wan Zhong Daoming and rasped, "Master?"
It wasn't his imagination. The look Si Mo gave him made it seem like he wanted to devour him whole.
The System hurriedly popped up: "I've rolled you back! Please, you must stop Si Mo from going demonic! Muah!"
When Wan Zhong Daoming opened his eyes again, he had returned to two hundred years earlier, just before he was about to meet the young Si Mo. The place from his memories, the filthy little brat from his memories, and that look from his memories, the one that said he wanted to devour him whole.
And the resolute vow in Si Mo's heart: In this life, I will protect Master at all costs and make you mine!
While Wan Zhong Daoming was still stunned that he could hear other people's thoughts, he discovered another thunderous truth: the Demon Venerable Si Mo was back.
And he wanted to sleep with Wan Zhong Daoming every waking moment.
Wan Zhong Daoming: ...Thanks for asking, but he has no interest in being won over.
They dote on each other; the shou has a secret crush on the gong; older love interest [raising him]; a little angst spices things up.
Qi Refining → Foundation Establishment → Fusion → Fasting → Golden Core → Nascent Soul → Mahayana → Deification
Many original worldbuilding details. Screenshot dated 2021.11.23
Theme: What the heart yearns for, the body pursues, and in the end, it finds its way home.