Demon Disassembler

Demons from another plane of existence suddenly swept across the world, and human civilization fell into twilight. Only a few survivor bases still held on to the last glimmers of human brilliance.

He Xu, separated from his family and missing part of his memory, was rescued and brought to a survivor base after narrowly escaping death. For some reason, he seemed to know the anatomy of demons exceptionally well. Before long, he had found a job at the base that could keep him fed: demon dismantler.

While he was busy breaking down the demon corpses brought back by demon hunters and selling the materials to auction houses, one demon's "corpse" suddenly came back to life and shouted at him:

"Doctor, run!"

He also discovered that the powerful demon hunter Ran Yue, who had always protected and looked after him, was hiding a great many secrets. It seemed Ran Yue had been trying to control him all along, and even... wanted to possess him.

Probably a calm, crazed, motherly top X an innocent, obedient, even crazier bottom.

Theme: To save the world, start by saving yourself.