Looking for a manga where the main protagonist is seemingly good for nothing guy who does not stand out from the crowd. He does not like violence and prefers quiet and peaceful life. Therefore, he's not popular among classmates/comrades/colleagues as he's too boring to even pick on (I'm not going to limit the genre of manga. Let it be school life, martial arts or even romance).
In reality, the protagonist is actually a complete badass with a calm and collected mind who have gone through/seen some serious s*it in the past and tries to leave it behind him. He's more powerful than most people surrounding him but he does not show his strength and is not drunk with power - let say he's more mature than other's in his age.

Of course, things change and all comes out eventually. Be there some kind of incident where he has to reveal his true colors to protect other and lot of people or let say only one girl finds out his true nature.

One good example of similar character is Himura Kenshin from Rurouni Kenshin. Ok, not exactly the same but I really liked his character.

Sorry if there are too many criteria to meet with this request but hopefully there are mangas with similar features out there.

Mob Psycho 100 comes to mind.

It's written by ONE, who also happened to create One Punch Man.

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mostly angry, always witty

Dendrobates

To a lesser extent, because they become more famous as their true abilities are being relied upon more:
Black Haze
Mahouka Koukou no Rettousei

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Nulla in mundo pax sincera
"Always go too far, because that's where you'll find the truth." - Albert Camus

Many thanks,
I started reading Dendrobates and Mob Psycho 100. Will also check other suggested mangas.
Any more suggestions related to school life for example?

Samurai Deeper Kyo comes to mind. At least in the beginning (any more would be spoiler).

Thanks lailacampos, will check it out.