Emperor's Domination (Web Novel) - Chapter 6624: Heaven Break Variation

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.

A teenager named Evan Mason was reincarnated into the magical world of Harry Potter and goes to school at Hogwarts!
With only his knowledge of the future and great talent for magic, he takes the path towards the top of the magic world, only to realize that ever step he took, changed everything!

- Description from Novelupdates

In his old world, Elric had nothing—no powerful family, no elite degree, just relentless hard work and a passion for healing. Dismissed as a third-rate doctor, he shocked the nation by saving a congressman’s life and becoming an overnight celebrity. But just when his career was rising, tragedy struck.Now, Elric opens his eyes in a world unlike any he’s ever known—a land of swords, sorcery, and strange beliefs. Reborn in the countryside of a magical kingdom, where even a common cold is blamed on spirits, he’s the only one who understands how the human body truly works.With no palace, no power, and no one to trust, Elric sets up a humble clinic in a rural village. Armed with science and sarcasm, he treats the sick, challenges ancient traditions, and slowly earns the awe and fear of a world ruled by magic.Mocked as a fraud. Hunted by rival healers. Feared by nobles and mages alike.But this world is about to learn—Even a third-rate doctor can change history.

She was originally the young miss of the Marquis Estate, but became a peasant girl due to a mixed-up at birth.