Legendary Battle Pet - Chapter 3 - Evolve

As a promise, he went out into the world as an assassin. 3 years later, after becoming the Supreme Assassin, he gave up on everything he had and returned to the ranks of ordinary people. But one day, Kismet, a mystical game created by the National Research and Development had appeared.

As a golden dragon raised by a human family from a young age, Noah has no particular hobbies except for cultivating kings.Though some ignorant scholars misunderstand him, labeling him as a mentor of king slayers and trampler of royal authority, over the millennia, there are also wise men who praise him as the imperial dragon and holy dragon.Moreover, the vast empire's many races regard him as the pioneer of the golden age, an immortal radiance of the empire, eagerly desiring his regency and control over the empire's authority.

A teenager named Evan Mason was reincarnated into the magical world of Harry Potter and goes to school at Hogwarts!
With only his knowledge of the future and great talent for magic, he takes the path towards the top of the magic world, only to realize that ever step he took, changed everything!

- Description from Novelupdates

[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.