Quills: the Rise of the Northern Matriarch - Chapter 6: Misunderstood

Once upon a time, an Alchemist Grandmaster from the World of Immortals accidentally took possession of a playboy, who hailed from a rich and powerful family, and became a student in the middle of his midterms.

Reborn in 2004, facing the age where pigs can be blown up, Lin Xuan, carrying the “Strongest Cottage King System”, started galloping…

- Description from novelbuddy

Waking up in the body of a 6-year-old boy a few years before Cintra is destroyed, Madara receives a system that gives him the ability to gain the powers of Uchiha Madara.[The peak of Uchiha Madara's system is before he becomes the ten-tails jinchuuriki.]The system's percentage does not stop Madara's power, but rather the system's release. After all, I don't want to see a character who goes around killing everyone from the beginning of the story.

I finally managed to kill the demon lord.