One Piece: Dream of Immortality - Chapter 12: Setting Sail

She is a descendant of an Ancient Chinese Aristocratic family. Having just transmigrated into a young lady’s body filled with aphrodisiacs, she had no choice but to pounce at a random man upon arrival.

The word defeat did not exist for Wei Congying in his relationships.

But the biggest joke was after the prodigal son returned and realized he was someone else’s stand-in.

Three years after breaking up, while sitting in a fast food place in the Isle of Mann, he saw her and discovered an something even more laughable…

He was still in love with this heartless person.

- Description from Novelupdates

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 story of time-travel. Sly and cunning, she unexpectedly became a sickly noble lady whose fiancé is merciless and demotes her to a lowly concubine. She sneers and bravely breaks off the engagement. To hell with scumbags, marry heirs to lords, blind the courts with her brilliance.