Avatar - Conquering the Elements - Chapter 3. The Spirit of Knowledge

The little handsome son-in-law passed through a world as waste material and the husband of a wealthy family. But because of his lacking aptitude, the wealthy family had driven him out. So he worked hard and found a more powerful family’s thighs to hold onto. Soon enough, he became the strongest son-in-law and husband in history.

In this world, it was impossible to practice martial arts. It was futile so he might as well take advantage of his wife’s thighs and maintain a comfortable and leisure lifestyle.

He’ll train his wife to become the strongest and best person in the world.

“Whoever dares to provoke me, let my wife kill you!”

- Description from Novelupdates

Kurogami Ichiro was desperate because he couldn’t achieve what he wanted when he once started his martial arts path at age of 8!

In a world where power defines worth and survival is a privilege earned through strength, Ronan was just another broken soul—bullied, beaten, and forgotten.Until he snapped.[System Activated][You have acquired an S-Class Ability: Starflame][Extreme rage and deep-seated hatred detected][You have obtained the unique skill: Devil’s Covenant]Once a victim, Ronan begins to rise—with a system by his side that grants him power through every action.When he cooks:[Skill Acquired: Home Cook]When he reads:[Skill Acquired: Speed Reading]When he fights:[Skill Acquired: Vital Strike]And these skills?They evolve.[Skill Devil's Covenant has upgraded into Devil's Divine Judgement][Skill Speed Reading has upgraded into Hyper Comprehension][Skill Energy Slash has upgraded into Demonic Slash]Every moment, every breath, every choice brings him closer to power.A hero, or a villain?He stands among them.

For the wine to be drunk on her wedding night to actually have been a cup of poison and for the one to poison her to be her husband, who would believe it?