Humans

Humans (人間, Ningen) are the dominant race in the world, as they outnumber all other races.

Overview
Humans, also known as  Homo sapiens  (ホモサピエンス, Homosapiensu) are a race of sapient bipedal primates that inhabit the world of One-Punch Man. They are the dominant and most abundant species of animal on the planet.

Human size vary according to it's ethnicity and age. Humans possess skin color which ranges in variety from the darkest brown to the lightest hues. Certain body parts, mostly facial structures of humans vary a lot from ethinicty and age.

A running gag in the series is that a lot of humans are unable to accept Saitama 's immense strength despite witnessing him in battle. For example, they call him the fraud after he defeats the Sea King despite he one punches the monster as well as clear the rain away at the same time. Another time is when Saitama battles Suiryu in the Super Fight, despite no one in the security staff are dared to intervene Suiryu fight, they willing to pin Saitama down and capture him without a slighted thought that Saitama is unfazed by Suiryu's brutal attacks and was the one who defeats him in the first place. All these factors indicates that the majority of human suffers from Sunnydale Syndrome.

Furthermore, human also cares more about the reputation of the person without taking into consideration of their true power. Only the handful of people like Bang, Murmen Rider or Suiryu are perceptive enough to determine the true power of the person.

Plot
Humans appeared on the world in an unknown period of time. They were the dominant species in the world prior to 15 years ago, when a race of creatures labelled Mysterious Beings appeared and started creating havoc and killing humans. At first they could be easily dealt with, but with time Mysterious Beings grew stronger in power to the point regular weapons became useless against them. In order to fight the Mysterious Beings, the Hero Association was created.

Abilities & Powers
Humanity's main power is its intelligence and numbers. They vastly outnumber the Mysterious Beings and possess advanced technology which allowed them to multiply across the planet. However, most of the weapons they use prove to be useless against stronger Mysterious Beings.

Humans defend themselves from many of the stronger Mysterious Beings with the heroes from the Hero Association. Mysterious Beings ranked as wolf and tiger are still dealt with using regular weapons.

'''The following section contains webcomic spoilers. You have been warned, manga-only readers.''' According to Dr. Genus, every human is born with a natural limit. Once this limit is surpassed, a human gains the potential to manifest incredible power.

Trivia

 * It's hinted by Dr. Genus that Saitama's powers were granted by breaking his human limits.