One punch man webcomic is a webcomic created by ONE about the the adventures of the hero Saitama. This is the original series of the manga One punch man, and thus, is where it gets most of its source at.
After the introduction of Saitama defeating Vaccine Man and Beefcake, Saitama's past is shown, explaining his decision to become a hero.
The first section of the story follows Saitama and Genos in their fight against the House of Evolution, where Saitama fights against Asura Rhino and wins nonchalantly.
After taking up arms against the Paradise Group, Saitama meets Speed of Sound Sonic, who declares Saitama as his rival after his defeat.
Saitama and Genos join the Heroes Association, with Saitama placing low in the ranking due to his awful score on the written portion of the entry exam. Saitama and Genos begin life as true heroes, with Saitama struggling to maintain his position as a hero due to not reporting any work to the Association. After a run-in with Speed of Sound Sonic, he incapacitates him and reports it to the Association, who lock Sonic in prison.
After defeating Kombu Infinity, Saitama takes a break at home while Genos is called to a meeting among S-Class heroes. The top heroes are called to arms to defend against an impending meteor impact. In the end, he, Bang, and Metal Knight are useless against the huge meteor, resulting in Saitama stepping forward to destroy it. Due to him having been in proximity of S-Class heroes, he recieves only a portion of the credit, and other heroes begin to dislike him due to thinking that he uses the work of others to ascend in rank.
The Sea Folk emerge, led by the Sea King, against humanity. Speed of Sound Sonic, with the help of S-Class hero Pri-Pri Prisoner, escape prison and attempt to fight the Sea King. Everyone that goes against him is defeated. Genos attempts to stop him from destroying a shelter and killing the civilians within, but he is defeated when he uses himself to shield a girl from the Sea King's corrosive saliva. Liscenseless Rider falls in a valiant attempt to stop the Sea King, but is caught by Saitama, who proceeds to kill the Sea King with a single punch. The civilians, initially shocked and in awe of Saitama's power, are once again turned against him when he states that he took credit from the real heroes again in order to maintain the heroes' image.
Saitama joins the S-Class heroes in a meeting during which the Dark Matter Thieves attack and destroy A-City. Saitama enters the massive ship while the S-Class heroes partake in battle against Melzalgald, one of the three strongest underlings to Lord Boros. Saitama begins tearing the ship apart from the inside before reaching Lord Boros and initiating battle with him. After a lengthy battle, Saitama becomes jaded with the fight and goads Boros into unleashing his strongest attack, which Saitama blows away with his Serious Strike, the force of which mortally injurs Boros, who states that Saitama is too strong before dying.
Saitama becomes friends with King shortly after when the former realizes that the latter is not as strong as he is made out to be, but does not mind. During this time, many villains and outlaws are called to the Heroes Association HQ to be asked to join together to protect the Earth from future threats. Among them is Garou, Bang's former top disciple, who claims that he will become the ultimate threat, and proceeds to kill all villains and heroes present, beginning a hero hunt.
After a lengthy hunt, Garou himself is hunted by Bang and his older brother, Bomb, who beat him mercilessly before they are attacked and incapacitated by a group of monsters from the Monsters Association, who take Garou with them. They state to Garou that they will keep him if he kills a human. He fails this by instead helping an ugly child that was being bullied. The monsters attack him but fail to kill him, only knocking him unconscious.
The Heroes Association becomes aware of the Monsters Association HQ in Z-City, and begins an infiltration at the same time as Garou. After multiple lengthy battles, Tatsumaki reaches the leader and rips the entire base out of the ground. She then begins battle with the remaining monsters, but is overtaken by them to an extent before Garou appears, having become immensely powerful from his many battles, evolving into a borderline monster himself. Garou incapacitates multiple S-Class heroes and monsters, then taunts the heroes that are unable to fight, stating that he will kill the child he had once saved from being bullied.
At this point, Saitama approaches him with a complaint that he is being a disruptive neighbor. He states that he is going to beat some sense into Garou, who attacks with the thought that Saitama cannot withstand the attack. The result is that he is hit with a punch that sends him skipping across the ground. Garou utilizes his martial arts prowess to briefly appear to be overtaking Saitama, but Saitama grows bored and tells Garou to truly fight all-out, demonstrating how serious he himself can be by flipping the entire Monsters Association HQ once again.
In the debris, Garou becomes disoriented and is beaten badly by Saitama. Upon landing on the ground, he becomes frustrated and more desperate, trying to damage Saitama in any way that he can. When he fails to and takes another powerful hit, he evolves into a complete monster and attempts to attack Saitama, only to be defeated in one punch, resulting in another evolution that is swiftly dispatched as well.
After a long spiel about his philosophy, Garou demands that Saitama explain why he is a hero. Saitama's simple answer irritates him into yelling more, and Saitama shatters the remaining monster left on Garou in frustration. He then states that Garou had an ideal image of a hero in his mind the entire time, and suggests that Garou wanted to be a hero the whole time, but lowered the hurdle at the last second to become a monster that simply had to kill every hero and unite the world against him.
The heroes attempt to kill Garou, but Saitama stalls them and Bang attempts to punish Garou. After the child Garou saves intervenes, Garou becomes filled with a desire to live and flees the scene.
The Manga adaptation of OnePunch-Man is illustrated by Yusuke Murata and follows the adventures of Saitama. While being almost exactly the same series in terms of content there are slight variations and the artwork is a much higher quality. The Manga is published by Sheuisha's Young Jump Next and has several volumes to it's name.