The Butcher of Gadobhra - Chapter 282: Merchant War

Xia Yan passed through to the world of Bleach and became an eleven-year-old boy. He was rescued by Renji and Rukia in the Seireitei, and he was studying at Shin’ō Academy, and he was a student of the same class.
He is a top student of the Shin’ō Academy, and he is vying for strength by various teams. In the end, he has entered the first team of secret mobile maneuvers.
He will use punishment to kill every person who tries to threaten the martyrdom and protect his loved one.

- 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.

I was always alone, throughout my life. People looked at me with disdain because I was an orphan without parents. Constant abuse followed me everywhere. I lost touch with how to interact with others.With each passing day, I grew more distant from my emotions until I scarcely recognized myself. The warmth of family and friendship felt foreign to me.In the end, I snapped, and I became what I hated the most... something that wasn't human anymore... something that shouldn't have been born...That was until I was reincarnated as Lucas Nightstar, granted a second chance at a happy life with a loving family. Now, I would do anything to protect them, live my life to the fullest, and was willing to destroy anyone who dares stand in my way of my newfound peace. Yet...Little did I know what fate had in store for me.

When people die, where do they end up to?I don't know about anyone else, but when I died, I arrived at the strangest Heaven of all times. And I got a chance to reincarnate with all of my memories!Jackpot!If you look away from the fact I had to reincarnate as a damn monster which is the lowest of all the bottom feeders? And I had to represent one of the worst goddesses ever!?And to make things worse, my “birthplace” was a freaking Dungeon! And not your everyday Dungeon with level 1 slimes and goblins, but a freaking Dungeon-turned-world-destroying-facility!Still, you gotta work with what you have. So see me how I survive in this crazy new world!!...But I promise I won't be mad if the bosses get debuffed. No? Damn...