One Moo'r Plow - Chapter 14B2-: Iron is the Hand II.

When Song Qinghan woke up, he found that he had not only transmigrated into another world, but also… had a ball in his stomach. He thought the original owner of this body had left a total mess to him. But it turned out there was a piece of precious jade hidden in it. Looking at the six-pack abs of Wu Dahu, he rubbed his hands with great excitement. Farming, your job! Hunting, your job! Giving birth, ahem, you worked hard! But surgery… leave it to me!

This stands at the forefront of strategy guides to Life (a shitty video game)!

The formless ancient world was infested with despicable demons. They hunted and feasted on mankind, keeping the human civilization constantly in a weak and suppressed state.