JoJo: An Ordinary Office Worker in Stone Ocean

He accidentally transmigrates fifteen years into the past, into Diamond Is Unbreakable, and becomes the villainous boss of Part 4, Yoshikage Kira. To his surprise, he arrives at the exact moment in the manga when Kira is hiding under the bed, preparing to assassinate Reimi Sugimoto! Then the serial killer Angelo shows up at the apartment. Kira drops the knife in his hand and solemnly tells Reimi: "Miss, don't be afraid. As you can see, I'm here to protect you!" ... (P.S. Starting with Stardust Crusaders, Parts 7 and 8 will also be gradually added~)