One Piece: The Justice of the Supreme Ruler

The protagonist defended Garp, so internet trolls called him a Garp fanboy. How could he put up with being insulted? He fired right back at them, only to transmigrate into Sengoku just after his battle with the Golden Lion. As a transmigrator, he naturally had a System. But this System was a bit of a rip-off: he had to wait until he turned sixty and retired before he could use it properly.