Nidome no Yuusha - Chapter 127 - Countdown to Outbreak

“Marry me, and you might not live to regret it.”Everyone in the city knew about him—a ruthless tycoon with a dark reputation. Whispers said he was cursed, having outlived four fiancées, each meeting a tragic end. When she became the fifth, forced by her own father to take her sister’s place in the marriage, the city waited for the inevitable. They were certain her body would be carried out of his mansion within a month.But to everyone’s shock, not only did she survive—she thrived. From a pawn in a deadly game, she rose to become the most formidable woman in the city, turning the tables on fate and rewriting her destiny.

A girl who calls herself a demon appeared before a timid student named Fumio Kijima. The girl claims to be a campaign girl from the demon world and she gives him the ability to “summon a room” from nothing but thin air.

At first he doesn’t abuse his power and uses it as a convenient ability in his every day life. But one day he is bullied by his classmates under a false pretext and is made to suffer. In the past he would have wallowed in misery and cried himself to sleep, but now he had a power to call upon.

“I will make them regret it!”

Using his powers to summon his “room”, he begins his era of confinement and brainwashing to achieve his goals.

He rose from abjection and achieved eternity in glory.
He embraced the prettiest beauties and killed the strongest opponents.
He was able to shift the clouds into rain and cover the sky with one hand.
He could overrun the entire world and go anywhere as he pleased.
He pacified wars and held the world in awe.
He was matchless in the world.
However, his hair turned white overnight for his beloved woman and he was on the verge of death.
He was surrounded by enemies who were trying to take his life.
He struggled his way to become mighty and fought for everything he cherished.
For this age, he was the only king of the Dark World.
His name was a byword for might.
As a man living in the world, his only ideal was to pursue brilliance.

- Description from Novelupdates

I’ve become a rogue lord in another world! This is the story of a game I was playing! The story of the protagonist, who has become a rogue lord who dies after two days, successfully uses the game’s history and system to escape his impending doom and become the strongest.