Heroes (ヒーロー, Hīrō) are individuals who fight for justice against all evils in the world. They also protect innocent civilians from any harm against natural disasters, Mysterious Beings, Villains, and other threats. Most heroes are registered with the Hero Association and are divided into four classes: From lowest to highest, there's C-Class, B-Class, A-Class and S-Class, each having their own individual numbered rankings within the class. However, the Rank 1 heroes of A-Class and B-Class are substantially more powerful than the bottom-ranked hero of S-Class and A-Class respectively; they chose to keep their Rank 1 position in their current class as a gatekeeper, or for reasons of their own.
There are numerous unnamed heroes.
S-Class (S級, S-kyū): The highest and strongest class in the Hero Association. Here are listed the most powerful heroes, who are said to each be at least as strong as an emergency army division. This class was originally created to gather individuals who, despite their low ranking, were capable of defeating disaster level Demon Mysterious Beings on their own. The current highest-ranked S-Class hero is Blast. There are currently a total of 17 heroes in this class, the lowest amount of members out of all the classes.
A-Class (A級, A-kyū): The second strongest class out of the four classes. When a hero reaches Rank 1 in B-Class, they can climb up to A-Class. Heroes in this class are considered very powerful and are often the most popular. The current highest-ranked A-Class hero is Sweet Mask. There are currently 38 heroes in this class.
B-Class (B級, B-kyū): The third strongest class out of the four classes. When a hero reaches Rank 1 in C-Class, they can climb up to B-Class. Heroes in this class do not have to perform weekly heroic acts to fulfill any quotas. The current highest-ranked B-Class hero is Fubuki. There are currently 101 heroes in this class.
C-Class (C級, C-kyū): The lowest and least strong class out of the four classes. Although C-Class heroes are the weakest, their strength exceeds that of an average person. When a hero enters the association, they normally begin here. C-Class heroes must perform weekly heroic acts to fulfill their quotas, otherwise they are removed from the Hero Registry. The current highest-ranked C-Class hero is Mumen Rider. There are currently 390 heroes in this class, the most numerous out of all the classes.
Unknown Class: Heroes whose Class and Rank are unknown.
- Both mangakas have been asked what kind of hero they would be in the world of One-Punch Man. Murata claims he would be a C-rank hero called Sakuga Nebukuro, who only collapses when he sleeps and draws pictures in his sleep whenever he does. ONE said he would be a C-rank hero called Trash Collecting Man who collects trash.
- Genos is the first hero in 2 years to be recruited directly to S-class .