Zero no Tsukaima - Volume 2 Chapter 6

Payload specialist, Tang Yue, who is a mechanical and electrical engineer by training, is left stranded on Mars when he receives news from his AI robot assistant, Old Cat, that Earth has exploded. He believes himself to be the last human in the Universe.

Damien Julian is an 18-year-old loser, who has been bullied and mistreated his entire life, at home, he has to deal with his abusive father, and at school, he is constantly been bullied by delinquents, and to make things worse he is always looked down upon by his peers, till one day a mysterious screen appear before him as it said.

[The world has seen the lingering evil in your heart]

[Would you like to be one of the nine demon kings of this world]

[If so what are you willing to sacrifice?]

In the heat of the moment, Damien made a deal with the world, that he would give up everything he owns, or do anything it wants, and in exchange, he shall be reborn as a new Demon King, and what the world required from him as payment was.

[In exchange for power, become a slave of the world, and act as an anti-body for all eternity]

At that moment, Damien agreed, but little did Damien know, that becoming a slave to the world meant he has to be its immune system, what that entail is, that anything that threaten the world must be destroyed even if he has to wipe out humanity, to save it, or assassinate historical figures to bring fort balance or even manipulating events that can potentially end the world, to save the world, this is the story of a necessary evil, not the story of a hero who cares for others.

The end of all worlds approaches.

The Demon King Order harvests lives from all manners of living beings.

Within this darkness full of despair,
A single person escaped from space-time, returned to before the world collapsed, determined to change the fate of the past.

But as time pass, he gradually finds out that the Apocalypse isn’t quite as simple as he thinks…

- Description from novelupdates

In this world, human are in peril. 72 Obelisks suddenly appeared out of nowhere, infecting the world with Monsters. Amongst this chaos, people look for hope.

A man named Basil Pacifer is the humanity's hope. He is the strongest Mage alive at that point. Sadly, he believes in no man, and he always moves alone.

...

Basil observes the unfolding scene bitterly. He is aware of his impending doom, however he has no grudge. He has lived long enough to achieve things people can only dream about.

Looking back to his past, he realized his life is nothing more than a sad story.

Closing his eyes, he accepted his end — or so he thought.

...

”Look at me! What do you see?“

”Regrets.“

”Don't you want to undo it?“

”Tell me what the offer is.“

Thus, Basil Pacifer returned to the past, being his younger self once again. Of course, he returned back with something.

...

[Ding!]

[Guide to Omniscience is successfully merged with The Chosen One]

[Analyzing The Chosen One's mental capability...]

[Analyzation Complete!]

[Result: The Chosen One is retarded]

[Initiate Brain Configuration!]

No matter how useless the golden finger he received seems, he will reach a higher height than his last life. This time, he will completely erase any regrets he has!