UnOrdinary!
Black Haze
Lesser known but Dokgo is a pretty good one. There're twins. One is good, not into fighting. One is badass, fights and wins those fights. Unfortunate events happened to the good twin so the badass twin goes to take his place, pretends to be unskilled at fighting, and takes down one bully after another with his badass fighting skills. I wouldn't say he's extremely strong like Goku strong but strong enough to avenge his twin. I liked it alot when the bullies got bullied. Those bastard deserved it. I really rec.
Any manga reccomendations where the mc looks/acts/says they're really weak but then theyre actually a total bad ass and extremely strong? Kind of like Tiji-kun?