Assimilate All Talents - Chapter 22: C-Rank Dungeon

Her family used her, her boyfriend cheated on her and had an affair with her stepsister, and in the end, she was killed by them. But fate took pity on her and gave her a second chance in life, and in this life, she promised to reclaim everything that was stolen from her by those scums.

But who would have thought that in this second life, she would also meet him? She was spoiled and pampered by him so much that nobody dares to bully her anymore.

The world had started doomsday, and I struggled for a year, before I died under an enchanted beast’s claw. Heaven has given me another chance, back a day before the end happen. Will I be able to change my fate, and that of my loved ones? Now, I will start my journey on becoming the strongest on the planet that the Gods have changed into a game world.

- 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.