One Punch Man follows the story of Saitama, a hero who can defeat any opponent with a single punch. Despite his overwhelming power, he struggles with boredom and a lack of worthy adversaries. He seeks recognition and a challenge, joining the Hero Association in hopes of finding a worthy opponent. Alongside his disciples and friends, Saitama faces an array of powerful villains, yet his true struggle is often against the mundanity of his existence, as he searches for excitement in a world that he has already conquered with ease.
In the first major fight of the series, Saitama faces Vaccine Man, a villain who seeks to take over the world by causing disease and chaos. Saitama, with his overwhelming strength, defeats Vaccine Man with a single punch, showcasing his incredible power from the very start of the series.
Crablante is the first villain that Saitama defeats in the series. He is a mutated creature with a crab-like body, wreaking havoc in the city. Despite his monstrous appearance, Saitama easily defeats Crablante with a single punch, proving that he is already beyond most opponents.
One of Saitama’s most intense fights, Boros is the leader of the Dark Matter Thieves, an extraterrestrial race. With his regenerative powers and massive strength, Boros presents a serious challenge to Saitama. However, Saitama ultimately defeats Boros with his Serious Punch, breaking the villain’s regenerative abilities and ending the fight in a spectacular fashion.