Hagakure Sakura Does Not Lament - Chapter 85

A good-for-nothing man married a beautiful girl but was kicked off the bed on the wedding night. Furiously, he wrote a bill of divorce and ran away.
He was schemed a car accident in which he nearly lost his life. However, it turned out to be a blessing. He swallowed the soul that passed through the outer world, thus obtained superb medical skills and martial arts.
Later on, with the silver needles and invincible martial arts, he embarked on the road of counterattacks and was committed to his great dreams.

- Description from Novelupdates

In the wake of the Battle of Katze Plains, the banner of Ainz Ooal Gown flies proudly over the city of E-Rantel. The Sorcerous Kingdom has entered the world’s stage to the clamour of death and devastation; the surrounding nations fearfully prepare even as they reel from its calamitous debut. Within the borders of the newly annexed realm, its Human subjects cower in their homes as the Undead openly walk the streets and stalk the lands. Yet, when a destitute noble finds herself under the auspices of an unlikely benefactor, events are set into motion that will resound over the world for ages to come.A kingdom builder based on the events and setting of Kugane Maruyama’s Overlord. In a fantasy world where beings of matchless power are transmigrated from the arbitrary existence of a game, Valkyrie’s Shadow chronicles the lives of the natives whose reality has been turned upside down by their advent. It is the tale of a nation created by the whims of a supreme sovereign, and his unstoppable servants who each have their own, often twisted, interpretations of their Master’s Will. There is no victory in strength; no miracles wrought from magic that will save them: only the inexorable advance of a new world order where those who secure a place of service within will find themselves turned against the world that they once knew.[Slow buildup. Methodical storytelling with a focus on well-rounded kingdom building and character development.]

Kai was a 17-year-old dropout. A NEET. A background character in real life with nothing to his name but bitterness, novels, and guilt. After his parents died, he gave up on the world. People were fake. Dreams were pointless. And that one novel he kept reading? He hated it especially the main character, June. Perfect, noble, always standing tall. Everything Kai wasn’t.Then, one night, a voice asked: “What if you did meet June?”He said yes, half-asleep and half-mocking.Now he’s trapped in the novel. Isikeid. But he’s not June. He’s not a hero. He’s not even in the main cast.He’s an extra in the background of a world he knows too well and he’s had enough of watching things play out the same way. This time, he’s going to change everything. Whether the world likes it or not.

"When will people understand.... I'm only half insane?"