Toaru Majutsu no Index: Genesis Testament - Volume 1, Chapter 2: A Changing Academy City, the Night Before – the_24th,Showdown.

During one of our arguments, my younger brother taunted me, claiming that I only knew how to depend on guys to get me through MMOs. In a fit of anger, I was spurred on by his words and decided to defeat my brother without depending on anyone else. By some coincidence, a new game called “Second Life” was about to go on the market and thus I started from scratch as a player. What’s more, I was the first person ever to log onto the game. The beautiful GM told me that I could have one wish granted… Humph! I. Want. To. Become. A. Guy!

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

After 50 years of being in the position of Hwacheon Clan Leader, Kang-hyuk, widely renowned as 'The Dragon' retires.

Following a brutal and tortured death, a former assassin, known only by his codename Kuro, is given the opportunity to reincarnate in another world, a world with magic and monsters. Armed with an unrivaled healing factor and an inhumane pain threshold, Kuro opts to go for a reckless direct approach in this world instead of a stealthy and cautious one, and as a result, slowly gains attention bit by bit.

Having previously been a loner in his old life, he interacts and befriends people for the first time in his existence, however, his blunt nature also sees him making just as many enemies, both big and small. By combining his old assassin skills with the magic powers of this world, along with his high resistance to pain and rapid regeneration, he doesn't take long to establish himself as a formidable force in this world.

Initially, Kuro only faces minor threats, like weaker monsters and bandits. But before too long, the threats slowly but surely become more and more severe…from Zombies to a bloodthirsty empire to Vampires and Demons, and even divine beings…however, as the enemies he faces grow stronger, so does Kuro, gaining rare powers that have never or rarely ever been seen in this world…