Survival as an antagonist is hard when the world is against you

A remake of another novel I created. Kazuki Takumi Amagiri was always a kid with a troubled life—abusive parents, poverty, and bullying at school. It's the usual sob story that might be featured in a documentary about the early life of a serial killer. Throughout his life, he often wondered if the world hated him simply for existing. But through a series of events, he met his best friend and was introduced to a series of games where he found a spark of resilience in a character named Markus, one of the main antagonists of the book. Ten years later, Kazuki is a university student, living in a dorm with his best friend, and on the verge of completing his degrees. He had just finished playing the third installment of his favorite video game franchise. Life seemed to be going well; things were looking up. Then, in one cruel twist, it was over. No fanfare, no "going out with a bang"—Kazuki's life just fizzled out like a candle in the wind. Strangely, though, Kazuki's story wasn't over. He found himself in the body of "Markus" at the start of his story. How will this ironic twist of fate change the world at large? And more importantly, how will it change our main character?