MTL - My Brother-in-law is the Prince - Chapter 6 The Son of Heaven Shouguomen

The world had changed when the System arrived, alongside the Cataclysm that filled the world with monsters. The technology was gone, replaced by classes and skills that allowed the people to fight back. When Devon ended up as a Blacksmith, a class that didn’t grant Intelligence, he had to face the reality, that his old career that he loved - mathematical sociologist - was over. Instead, he had ended up as yet another discarded member of the production class, overshadowed by the existence of the System Shops to the point of total marginalization. But, what if all he needed was to reapply his scientific thinking to the System...

After self-sacrificing, Yuri transmigrates from an apocalyptic to an interstellar era, inhabiting a disabled girl's body. She enters a joint marriage with a similarly disabled SSS-tier alpha, gaining a share in an ore planet. Determined to help her husband regain leg function and reclaim his SSS-rank, their journey together unfolds.

Chang An is a sub-beast who, despite having the talent for the sword, did not have the constitution to support it. And his savior, Hua Yi, is a beastman on the run for his life.

This is a story about how two once innocent children had to grow up in such a cruel beastman world.

- Description from Novelupdates

Chang An, capital of Tang, the most powerful empire in the continent. A heaven wrecking massacre shook the city to its core. Amidst the incident, a young boy named Ning Que managed to get away, dug out from a pile of corpses along with a little girl called Sang Sang. Years passed, and since that day the two of them lived together. Together with Sang Sang they both entered the military, with plausible military achievements, they were recommended into the Scholar School, which began their miraculous journey.