MTL - Release that Man - Chapter 355

Leon was your typical guy, perceived as weak in his school because his skills hadn't awakened, even though they usually did at the coming of age. He attended the prestigious Milham's Magic Knight Academy, where snagging the top spot meant automatic entry into the esteemed position of a Magic Knight in the country. Unfortunately, Leon found himself in the lower caste, labeled the most useless student. To top it off, he was tossed into a class that served as a sanctuary for oddballs and delinquents. Yet, he couldn't care less, as becoming a Magic Knight wasn't his goal.Everything shifted when he crossed paths with Shredica, a woman hell-bent on becoming a Magic Knight at any cost. Observing Leon's lack of ambition and his apparent detachment from the academy's pursuits, Shredica saw an opportunity. She decided to exploit him as a pawn in her ascent through the academy's hierarchy.Yet, unbeknownst to Shredica, Leon was not the complacent, unremarkable figure she presumed him to be.

I got sucked into a novel full of villains and must tame them in order to survive!

A river song, triggered a legend of the rivers and lakes.
Tian Zun’s life motto: “My sword is the truth.”
Shen Lang’s life motto: “To serve people with morality, those who are dissatisfied are dead.”

- Description from uukanshu (translated)

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.