King of Beasts - Chapter 26: I Cant Teach You That

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.

She had never expected that she would slept with her deadly enemy,but it turned out to be a good match for both of them.

while after marriage ,his indifference finally angered her.

You damn bastard!

Chen Mu, a low-level officer, thought he could only live a cautious life, but unexpectedly he got a system panel that could accumulate experience, and he could master all the skills with just one practice.

[Blast Knife + Gale Knife + Wind Chasing Knife = Blast Artistic Concept]

[Jade skin grinding method + sand iron method + coarse salt method = skin of copper and steel]

A peerless martial saint with unparalleled swordsmanship, bronze skin and iron bones, and a body of pure gold was born step by step.

- Description from novelbuddy

The world was once at war with 10 alternate worlds. This was known as the Concept War and our world won 60 years ago. All of this was concealed so no normal people are aware of this fact in the current time.

After the death of his grandfather, the high-school student Sayama Mikoto is suddenly summoned by the giant corporation IAI. He learns this world is headed for destruction due to the acceleration of the Minus Concepts. To prevent this, negotiations must be undertaken with the survivors of the other parallel worlds so their 10 concepts can be released.

And so Sayama is caught up in the final battle to clean up after the Concept War which left behind so much enmity.