The Divine Nine-Dragon Cauldron - Chapter 10: Duke Xianyu

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.

“It’s finally here,” said the man with the sword in an echoing whisper.

“The Tower of Choice, the last 100 floors!” the band of five exclaimed in unison.

Angelica came down from the altar with a dull look, seemingly annoying.

Then we looked around.

“I tell you once again, but you’ve had a lot of trouble in the meantime. I couldn’t have climbed to the 100th floor alone without you.”

Thud!

One by one, they fall to the floor.

Angelica’s dagger pierced my neck, and I felt a darkening in front of my eyes with a tumultuous rage. My awareness faded, from my senses, from everything else. After that, everything was eroded by profound darkness.

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

The protagonist, a famous YouTuber known for playing the game trilogy “Tril Trilo Trilogy,” finds himself possessing the final boss of the game world.Before the release of the new instalment in the series, he receives an offer from the game’s developer to play a prequel, “Part 0,” which explores events that occurred before the first instalment. Since he is a fan of “Tril Trilo Trilogy,” he eagerly accepts the offer.However, through some twist of fate, he wake ups in the world of “Tril Trilo” in the dreadful body of the final boss of the trilogy, a character named Frank Wonderstein.