Suterareta Yuusha no Eiyuutan - Story 4-2: 『Demon King』

A lost soul from Earth transmigrates to a world of cultivation and finds himself in the body of a playboy noble and complete waste. Except he doesn't have any memories, can't let anyone know he's not the same person and is immediately involved in a conspiracy with a powerful noble family.Luckily he came to this world with a power, whatever he gives to someone as a gift he'll get it back 100 times better.His first target?His new wife, the former top young genius.

The world had changed when the System arrived, alongside the Cataclysm that filled the world with monsters. The technology was gone, replaced by classes and skills that allowed the people to fight back. When Devon ended up as a Blacksmith, a class that didn’t grant Intelligence, he had to face the reality, that his old career that he loved - mathematical sociologist - was over. Instead, he had ended up as yet another discarded member of the production class, overshadowed by the existence of the System Shops to the point of total marginalization. But, what if all he needed was to reapply his scientific thinking to the System...

This was the great era of vast warships and the Star River, a time when the multi-universe was shattered and countless Cosmic Fragments were scattered across the void, forming the boundless Shattered Starry Sea.Immortal Domain Dao soldiers, mechanical gods, golden giants, wizard Dominators…An endless array of strange civilizations.Starry Sea Oddity, Genetic Potions, exoskeletal armors, Floating Land Origin…Treasures that could be found everywhere.Spectral Shuttle, Spectral Airship, Spectral Warship, Escort Ships, Battleships, Star-Annihilating Starships, hyperdimensional mother ships…The clearly stratified Xinhuo warships.Song Chi held a Zhu Tian Ruins Market in his hand and engaged in interstellar trade with the countless peoples of the Starry Sea.What? Titanium Crystals are worthless in your Star Domain? I’ll take them all, damn it, this is a strategic resource!You call this a chunk of iron? This is Mixed Elemental Copper, the ultimate Enhancement resource!Ordinary ship cannon? Isn’t this a golden Star-Annihilating Cannon? Quick… I’ll buy it!…Stretching across the stars, starting from the flame of human civilization.

This is an extremely difficult game, if you don’t have enough skills, don’t even think about going out!

- Description from Novelupdates