Overpowered Archmage Doesn't Hide His Talent - Chapter 173:

Pinning her tall body against the hard wall, he looked into her beautiful emerald green eyes as he spoke in a deep voice, "I have two options for you," his body came closer to hers as he continued, "Be my girlfriend. Or," his lips turned into a sly smile as he whispered close to her ear, "Be my boyfriend." He even dared to wink right before her as his dark orbs glinted amusingly.

Violet skies, a world undergoing massive changes, a deficient moon, interlinking voids…

Chen Sha came to a world of immortal martial arts and was ordered to take charge of the world’s first sect.

Before his death, the previous chief told him:

“If you don’t become the best in the world for one day, you are not allowed to go down the mountain for one day.”

So he closed himself in painstakingly, crossed the heaven gate in his body, and faced off against the ancient and modern powerhouses…

…

Many years later, Chen Sha recalled the day he went down the mountain,

From the moment he descended the mountain, he was number one in the world.

In the next ten epochs, any gods and demons have returned, immortals and Buddhas have lived in the world, ancient powers and ancient gods have appeared one after another.

No matter how the times change, he has always been No. 1 in the world and has never changed.

- 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.