I'm looking for an action manga where the protagonist (or major character) doesn't have a sob story as background. S/he can have some drama in his life, but to the point of tragedy/trauma: ie. if his parents were divorced, both of them still shower him with love and adoration, if his grandpa passed away, it was because of old age. If he broke off his friendship with a childhood friend, it was over a toy or something similarly childish. Basically his past up to the beginning of the story must be peaceful in every sense of the word, and he will deal with incoming tragedy in the main plot without any emotional baggage or traumatic precedence.

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My list (rated by addictiveness, not necessarily quality)
Reading
Complete

possibly the manga that sparked this thread, but Onepunch-man

Hmm there are lots of protagonists like at least in shonen, here are a few not already on your lists. Keep in mind I tried to limit mangas to main protagonists that fit what you want, more often than not other MCs surrounding him/her do have tragic backgrounds :

Gate - Jietai Kare no Chi nite, Kaku Tatakeri
All You Need Is Kill
Black Lagoon
Hunter x Hunter
Mx0
Konjiki no Gash!!
Nurarihyon no Mago
Shijou Saikyou no Deshi Kenichi
Rising x Rydeen
Rave
Change 123
The God of High School
Kenji
BM: Nectar
Dragons Rioting