One Piece: From the Start, I Marry Kaido's Daughter Yamato

The soul of Su Jie, who came from Earth, had an accident and merged with Brad, a severely wounded boy aboard the Ohara evacuation ship. From then on, the world gained a man with a split personality. He formed an alliance by marriage with Kaido and gravely wounded Akainu, repelled Kizaru at the Sabaody Archipelago, and turned the Paramount War upside down. Two years later, the fate of Wano Country had been completely changed. (This book is told neither from the Marines' perspective nor the pirates' perspective, but from that of an Ohara survivor. The protagonist is a vengeful man who hates the World Government. A friendly warning: if you're a die-hard Akainu fan who thinks from the Celestial Dragons' side and believes everyone deserves to die, you may not even make it through the first chapter. I'm tired of explaining the protagonist's position over and over.)