MTL - I Bound Aizen - Chapter 6

He became a teacher at the best magic academy in the empire.
….For being mistaken for someone else.

A small skeleton in the undead world inadvertently passed through to the end of the world. His limited IQ found that his boss seemed to be weak. As a good value, he decided to protect the boss first. When he was annoyed, he would do it directly. Turn the boss to his own position. Gao Shuo inadvertently encountered a strange encounter. At first, he used this skeleton as a combat partner to raise it. Until one day, this skeleton became a man, and Gao Shuo made a new decision. Don’t hesitate to rush to eat. Meng pet sweet text! ! ! (Little Skeleton) The Lord is accepted by the Lord! ! ! The important thing is that the protagonist can be transformed between the monks and the people three times.

- Description from Novelupdates

Riven was nothing but a powerless runt until necromancers razed his village and butchered his sister before his eyes. As his blood soaked the dirt, his Sigil ignited, granting him a gift. He can die and reform, a cycle that resets with every rank he climbs.But fate wasn’t done screwing him.In the catacombs beneath the ruins, he found the Death Ledger—a death contract that bound him against his will to hunt those who’ve cheated death across dimensions. Historical legendary heroes and villains.From the noble King Arthur to the conqueror Genghis Khan and the fabled king of Uruk, Gilgamesh, together with Ivan the Terrible and Vlad the Impaler.Every mission is a gamble. Fail once, and the Ledger brands him a death-cheater, turning him into prey for the same immortal fugitives he hunts. And the reward? He gets to keep them as his undead summons.His enemies will not stop coming. They want the Ledger, the Sigil, his power. To survive, he will wield death itself, growing stronger with every soul he claims, because in a world this savage, only the relentless rise.[-Congratulations, you have successfully killed Alexander the Great and claimed him as your summon...you can start on the path of evolution-] The words, scrawled in blood, burned across the page of the Death Ledger.

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.