The Great Mage Returns After 4000 Years (Web Novel KR) - Vol 2 Chapter 378

It’s a affair between a loyal dog servant and his master.

- Description from Novelupdates

Merged into the body of External Disciple Chen Yu was the heart of a demonic god.The heart is the core of life, the most fragile vital organ. To Chen Yu, however, the heart was his greatest strength, granting him power and potential beyond demonic and divine beasts. Here on out, we follow him as he embarks on a mysterious and wonderful journey.

As a kind of punishment, the wings of a demon king were cut, and he eventually lost all of his power. To get back his power, he made a deal with the angel. He will go to the realm of humans to find a special girl with a special skill who is meant to be her queen. If the woman got pregnant, all of his sins would be forgiven, and he will regain all his powers. But he didn’t think that knowing her would be an adventure for him as the king of demons in the human realm.

[WSA 2025] To confront the threat posed by monsters and demons, humanity summons a hero endowed with a mysterious system and an unrivaled capacity for evolution. He becomes the last bastion of hope for mankind. However, one of his mistakes gives rise to a calamity far worse than the Demon King.This calamity is conceived in a dungeon, abandoned as a fetus by its mother, and raised by the Demon King himself. Upon the Demon King's death, all the restraints he had placed upon the creature are shattered. Thus, the hero's nameless son begins to lay waste to everything. The greatest calamity the world has ever known is born.