Magika no Kenshi to Shoukan Maou - 3.3.4 — The Silver Girl and the Plan of Darkness

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.

Karnak, a human born as an illegitimate child in a fallen aristocratic family, rose to the transcendent rank and became the Death King. Even god couldn’t contend with him.However, after becoming transcendent, he missed his human emotions, such as satisfaction and other things.So, with his oldest friend and second-in-command, who shared his belief, he decided to return in time with Barros and start over.However, something seemed wrong with this timeline.Now is the beginning of the new adventure of the Death King Karnak.

Jiang Chen, son of the Heavenly Emperor, unexpectedly reincarnated into the body of a despised young noble, thus embarking on the path of the underdog trouncing all commoners. No one has the right to call himself a genius in front of Jiang Chen, as no one has a better understanding of the heavens than the son of the Heavenly Emperor. “Genius? He who adheres to me shall ascend. Those who oppose me can find solace in hell!’

Legend says, that there is a great demon, who is the human kind’s public enemy. He is the galaxy federations’ nightmare as he wanted to conquer the whole universe. On the first day, he completely took out the human fleet, plunging them into disorder. On the second day, he declared that he will wipe out the whole federation. On the third day, he declared——that the hero who shot him in their previous battle must marry him, or else, he will destroy everything.

The galaxy federation president and the council members had a long meeting after that. They decided to dispatch a soldier, Wu Xing Yun, and marries him off to the arrogant demon. Wu Xing Yun was once a hero who fought for the nebula, and henceforth, he was tasked—— for the sake human race and the universe’s peace, to eliminate mistresses, settle his matters with the mother-in-law, and fix the man’s crooked ways.

Wu Xing Yun was very perplexed when he asked his commanding officer: “Sir, why did it have to be this way?”

Commanding Officer: “Soldier, bear in mind, that this mission of yours, is for the sake of the universe and mankind’s happiness. You must hold on to your husband, and fight other mistresses! Do you have the confidence to accomplish this task?”

Wu Xing Yun, stood straight, saluted, and instinctively replied: “Sir, yes sir! I will accomplish this task!”

- Description from Novelupdates