Ryo Takashi was just an ordinary high school student—until a clerical error enrolled him into Celestia Academy, an elite school for supernatural beings. Vampires, angels, demons, and gods-in-training roam the campus, each possessing powers beyond mortal comprehension. At first, Ryo is the odd one out, a powerless human in a world of legends. But everything changes when he awakens an ability unlike any other: Limitless Regression—the power to rewind time and redo events without limit. What begins as a desperate attempt to survive soon turns into an unstoppable force, allowing him to learn from every failure, perfect every skill, and outmatch even the strongest supernatural beings. As if being overpowered wasn’t enough, Ryo quickly becomes the most sought-after student in the academy. By ancient customs, his overwhelming strength makes him the rightful fiancé of numerous noble supernatural girls—each one determined to claim him. From a proud vampire princess to an enigmatic celestial heir, Ryo finds himself at the center of a romantic chaos he never saw coming. With endless retries, limitless power growth, and a harem of powerful fiancées, Ryo’s destiny is rewritten. But as ancient forces awaken and the world teeters on the brink of war, can an "ordinary" boy become the ultimate ruler of the supernatural realm?

A genius programmer, renowned for his ability to "debug" the most complex systems, dies in a freak accident when God accidentally presses the "delete" button on his soul. As an apology, God reincarnates him into a fantasy world and grants him an overpowered skillset based on his programming expertise, allowing him to manipulate magic, stats, and even reality itself like a developer modifying a game.