Read Full chapter: https://read-onepunch-man.com/
Well first off the one punch man webcomic is the original source, the manga is just adapting it for the casual audience.
The pictures on the left side are the webcomic, the pictures on the right side are the manga.
I mean, I have read the webcomic, and ONE (the creator of one punch man) is a good writer who has great ideas but lets be honest. His art isnt really good
Now, in my opinion the One Punch Man manga is the one we should consider canon. Becuase the webcomic is just “the rough draft” and just gives you a brief summary of whats happening but the manga is the “official” or “final” version.
The webcomic in my opinion is non-canon, but its similar to the manga. The manga actually improves the webcomic a lot.
For example, in the webcomic, Saitama surprisingly wasnt strong, and in the final fight Boros (in the webcomic) said he had a blast that will wipe Saitama off the face of the earth. But in the MANGA (with approval from ONE) Boros now uses an attack that is confirmed to destroy planets.
So in my opinion, the webcomic really isnt canon, but its super similar to the manga when it catches up.
The best way I can describe the One punch man webcomic and manga is like The Boys comic compared to The Boys television show.
Now, lets talk about the elepahnt in the room.
2. Orochi
In the webcomic, there is no Orochi. It was just Garou slowly becoming a monster, but there wasnt Orochi, the Monster King. But in the manga, Yusuke Murata created Orochi (with ONE’s blessing)
You get why I said “elephant in the room”? because Orochi is super huge?
Alright, I will see myself out now.
Personally, I think Orochi being in the manga is great because he’s pretty badass and actually plays a bigger role in the whole story.
3. Blast
In the webcomic, we actually dont see the world’s greatest hero, Blast. We hear rumors, but we only get shadowy glimpses of him.
In the manga, its completely different. SPOILERS FOR MANGA!!!
In the recent chapter, we actually see Blast
We dont just see Blast appear and talk to Saitama. We actually see Blast use his abilities
I also want to mention, that in the webcomic, Saitama and Flash never actually meet, but in the manga Saitama and Flash meet and talk.
I think the One Punch Man manga is probably 70 percent accurate to the webcomic. It’s the “definitive” version. You should still read the webcomic, as it kind of spoils the manga abit and is nice to compare the two versions.
Source: Quora
