Dragoon - Dragoon 86: the Battle Junky and the Protagonist.

One day, when a novelist woke up from a restless sleep,he realized that he had transformed into his 12-year-old self.

Gawain is dead and was transmigrated, but there was a slight problem during the process.
After floating for more than a hundred thousand years on a different continent, he felt that he might need a body to become a complete transmigrator, but he did not expect that…

- Description from Novelupdates

Yggdrasil, the World Tree of Norse Mythology, suddenly appeared on Earth. And with it came demonic creatures that ravaged entire cities.Although not all hope is lost, due to the System that a few special humans had gained.In this new world where only the strong survived, Min JaeHyun scrapes by regretting the wrong choices he’d made in the past… when one day, he gains the only Mythic item in the world.How will this item help him? And can he change his wretched fate?