Seirei Tsukai no Blade Dance - Volume 15, Prologue

A 30-year-old NEET is reincarnated into the body of an otaku that choked to death on instant noodles. As he comes to grips with his new life, he realizes that this world is subtly different from Earth. The denizens of this world are far better looking, and this new world also possesses futuristic technology as well as mysterious Yin Yang masters!

What’s worse than finding out you’re that Louis XIV when you’re a baby?

Of course there is, for example, it’s still a magic version.

- Description from novelbuddy

Nile Santos lived a life of sacrifice — always stepping aside, always giving others the best gear, always following orders without question. In the end, none of it mattered. His comrades fell, his body was broken, and he died a meaningless death in the final battle against an unstoppable force.But fate isn’t finished with him.Offered a second chance by the very beings who led him to ruin, he’s thrust back in time with all his memories intact. This time, though, he’s not playing the role of a noble shield. No more selflessness. No more obedience. No more being a pawn.Armed with future knowledge and a will forged in failure, he vows to rewrite his story — to take everything for himself. Skills, loot, allies, power… all of it. It’s time for one man to climb to the top, no matter what it takes.Author's other storiesThe Unrivaled Holder: Rise of the Dragon Monarch - 3rd Season OngoingI Ascend Alone - Ongoing

In a world fraught with innumerable dangers where living day by day is a struggle, a young man from the modern age transmigrated into such a world, accompanied by a peculiar system made for assassination.