Magus Reborn - 167. A war approaches

As a promise, he went out into the world as an assassin. 3 years later, after becoming the Supreme Assassin, he gave up on everything he had and returned to the ranks of ordinary people. But one day, Kismet, a mystical game created by the National Research and Development had appeared.

Enigmatic hands, spectral frame, and one cunning strike just like the swing of the Grim Reaper. The Supreme Assassin takes on the mystical world, and how his legendary tales sets off, progressively ascending the altar to becoming the best.

- Description from Novelupdates

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.

Revenge is a dish best served cold, with dollop of whipped suffering and a sauce of acute humiliation.Karma would do anything to exact revenge on the one who was responsible for her mother's death, her father's disdain and distrust, and a miserable life.She was manipulated, maltreated, and humiliated by the one she trusted the most. Her stepsister!!Discovering she had only three days left to live, Karma would go to any length to exact revenge. Even offering herself to the scary and powerful demon overlord.A contract. Blood oath. Manipulation. Betrayal. And lots and lots of revenge.