Hello! Try this story!
Title: Gray Scale
Description:
Eros Von Valix Silver resides in a remote area where most people earn their profit of living by planting crops, a village whose inhabitants are layered as the least important in the hierarchy of Winton Kingdom. It is a kingdom where superiority in terms of power rules.
In his hopes of elevating the area's status of living, he had a resolve to get stronger in order to eliminate those who look down on them and prevent wars.
"If power could bring the world together, then I must become the most powerful mage."
Achieving the level of power he wanted as a mage, however, required huge costs and risks. He thought he might suffer but he decided to never falter. Along the way, he had tough ropes to pull, but there were still no progress.
One day, he found this large cubic stone that was situated near their area. He thought it was a good spot for training as it was emitting enormous amount of mana from it. And so, every day he went there, training nonstop.
As smooth as things were going, he reached a level that nobody from their neighboring towns dared to infiltrate the area and challenged them. He was also able to raise the economic and noble status of the place, wherein even barter chose them as the most special client.
And there, he had it. It was indeed true that an unyielding power could change their whole situation. However, by the time he turned 18, everything changed. When the sun was about to go off the coast and when he was doing push-ups and a few crunches, a voice of a man called upon him.
"It seems your soul is now ready to receive my inheritance. Remember this. I was once the Martial Demon King, the one who rules the demons of the underworld. You should be grateful, Eros. It is now your turn."
Link: https://www.webnovel.com/book/gray-scale_17497678805174905#review
The MC here is totally overpowered. I can guarantee that part.