Beastmaster of the Ages - Chapter 4009 - Weak Link

Humanity has been gradually transported to the Abyss by a bored god to compete against other races and monsters.The problem is… humanity failed. In a last desperate push the strongest survivors chose a comrade to travel as far as possible back in time.

Protagonist travels between different anime worlds to right wrongs and uncover his reason for being along the way.

​The world, Earth, was devastated by the Great Incursion, an apocalyptic invasion by dimension-hopping monsters. Humanity's only hope now lies in Galaxy Fall, a newly accessible parallel world where they can gain strength through a System of quests and missions.​Five hours after the Invasion, the betrayed survivor Mirabella is mysteriously reborn and gains a unique power: the [Master Account System].Her initial skill is the deceptively simple but devastating 'Multiplier x100', which applies a 100 times buff to all her offensive capabilities, including physical attacks, spirit energy skills, and damage-over-time effects.​Mirabella must now transform from a silent survivor into the world's most feared warrior, who was only scared of one thing, which is?“I Hope I don't run out of opponents in Both worlds.”

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.