MTL - The Counterattack System is Only Available In the Mahayana Period - Chapter 580v2 create a song

mc gets transmigrated to Fallout New Vegas with the merchant system. let the questionable adventure begin.

[The 3000th Descent of Mystery is about to begin.][This is your only chance to redeem yourself.]When the whole world was in danger, Wang Teng activated a unique talent.It was the Rank SSS talent - Inequivalent Exchange!He was not purchasing things for free, but the exchange was not equivalent.[Exchange successfully. You used half a bowl of cup noodles. With your Rank SSS talent, you may retrieve an unlimited supply of cup noodles.][Exchange successfully. You used a bottle of Sad Breeze wine to exchange for the Star Shifting Method.]…From then on, Wang Teng activated a new exchange system.

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.

Reborn into the world of Yugioh, it's natural if my goal is to become the best duelist!