Skybound Throne - Chapter 96: The Cave III

The world that nurtured the civilization which reached the pinnacle of magic was on the verge of destruction.
The last survivor transmigrated to the past, when the magic civilization started growing, as countless mages were still fumbling their ways through the thorny paths of magic knowledge.
He, who came from the end of the magic era, aim to reach the pinnacle of magic.

- Description from Novelupdates

I couldn’t even clear the 2D version, now to clear the game in reality?Maybe I’ll have to live here for the rest of my life.Well, even that won’t be easy.– A player found himself in the game, Dungeon and Stone, as a savage barbarian.To keep his secret, he must become the mask – must make himself be seen as more savage, more fearless than any others – a paragon of his race in the eyes of the whole world.Back on earth, in the empty darkened room, the quiet computer again began to whir. Text began to appear on the black screen.「Synchronization complete. 」

Dying at a young age after a disappointing life. Mat thought he hit the jackpot when he got reincarnated on a tropical island as a baby. Here, exploring mysterious lands and learning magic are a reality. The world of Elydes is beautiful and magical, wild and savage. While the Guide is impartial to all, people are not. Mat has the lowest starting point possible, and those like him rarely go far. To not let his humble birth define his life, he'll need to find the determination to grow stronger and delve into the mysteries of Elydes.

Karl Adelheit, a self-proclaimed ordinary student returning from military service.

And a nobleman who enlisted as a soldier and received Medals of Honor.