Why the bug I wrote became a core gameplay mechanic?! - Chapter 6 - : There’s a Bug in the Game!

Year 2056, in a city in the Yuan Jiang Su Jin area. On top of a ruined, shattered six story residential apartment sits a teenager wearing a combat vest, militaristic trousers, and alloyed battle boots. On his back is a hexagonal shield and equipped is a blood-shadow battle knife. He sits there silently on the edge of the roof. At this time, the sparkling sky was shining and there was a refreshing breath within the air that blew towards him. However, there was only silence within the ruined, deserted city, with an occasional howl that makes your heart skip a beat.

- Description from novelupdates

Betrayed. Exiled. Murdered. Reborn.In the war-torn land of Glory, power is everything and Duke Merlin's bastard son has none. Cast out to a starving border town beside the cursed Devil Forest, Kaelor and his mother were meant to die quietly.But when assassins take her life and leave him bleeding in the mud, another soul awakens within him one from another world.And with it, something else awakens too...The Fusion System.A power that lets him fuse nearly anything.Fusing one starving soldier with a dead direwolf gave birth to a Dreadwolf Trooper.Fusing one hundred wild dogs produced the monstrous Cerberus.Fusing two crumbling forts created a living fortress bristling with autonomous ballistas.From broken men and dead beasts, Kael will forge an army the world cannot understand and a dominion no one will dare challenge.

220 years ago, in the legendary Dragon Demon War, Hero Azell ended the war by killing the evil Dragon Demon race’s King Atein. He was able to save the population, but as a consequence, he was cursed. While he was dying, the high magician suggested a gamble that might save his life.

I was reincarnated into another world, and I’ve brought the Horadric Cube from Diablo II with me.
Being a knight is cool and all, but being a wizard is pretty neat as well.
So, which one will it be?