Arifureta Shokugyou de Sekai Saikyou (WN) - Chapter 399

When an era came to an end, various forces set foot in cultivation to compete for immortality. A young boy who spent most of the time sleeping got lucky in the troubled times and became an unparalleled immortal who could cover the sky with a snap of fingers. Was he going to live forever?

- Description from Novelupdates

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

Long Fei, a cross-timer and doujin, is an otaku who traveled to another world. In the original world, he was an otaku fan of Gundam and military science fiction.

He died in an accident and was reincarnated into another world. The Gundam works he had read before his death and the techniques in various military novels could be brought to another world.

How would he use the Gundam that Long Fei created? What waves can be caused in this different world?

Birth rates are decreasing. Hope is vanishing. The world has gone gray.Humanity, drifting in quiet collapse, receives an email.Every person on Earth. Simultaneously.The Aegis Mandate.Disguised as a cosmic aptitude test, it triggers The Incident of Separation—a global psychic cataclysm that erases identities, wipes memories, and divides all survivors into three factions: Law, Neutral, and Chaos. Overnight, cities become battlegrounds. Apartments become dungeons. Ordinary people become monsters—or the ones who hunt them.Ragnar Vhagar was just a loner university student. Now, thanks to a system he didn’t ask for, he’s a newly minted Demon King, locked in a crumbling apartment with goblins under his sofa and a glowing soul crystal next to his frozen peas. His new job? Build a deadly domain, defend it from invading “Heroes,” and somehow level up fast enough to not die.Alongside him is Isabelle Thorne, a razor-sharp warrior of few words and one very sharp sword. Their reluctant alliance, born in blood and snark, evolves into trust—and maybe something dangerously close to affection—as they rise together through the layers of the game-like world they’re trapped in.With each conquered domain and defeated boss, Ragnar realizes the truth: the dungeons aren’t meant to crown a winner. They’re meant to break the players. The Law faction wants control. The Chaos faction craves destruction. But Ragnar? He wants something they’re all too afraid to say out loud:Freedom.In the ruins of Kanta’s ogre stronghold, Ragnar and his misfit warband take their biggest step yet—claiming a kingdom, unifying a fractured system, and preparing for what comes next. The Heroes are watching. The gods are stirring. The world is watching a war.And somewhere deep beneath it all... Ragnar is rewriting the rules.