MTL - Marvel: Anime Extraction - Chapter 412 High Priest of Sovereign

Paju, the city of hope, peace and madness.And the tale of a mage trapped in a bizarre world.“In his house at R’lyeh, dead Cthulhu waits dreaming.”

Fear breaks the boundaries between dreams and reality, and it is impossible to tell which is reality and which is illusory. When the nightmare really comes, no one can be alone.

This is both a danger and an opportunity.

- Description from novelbuddy

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.

My old man pointed to the flower-like woman and said, "Call her mother from now on." He then pointed to a flower-bud-like girl and said, "This is your little sister."