One-Punch Man season 1 follows Saitama, a bald hero who can obliterate any opponent with a single punch. Bored by his overwhelming strength, Saitama seeks a worthy challenge. We flashback to see him train relentlessly to become a hero, with the unfortunate side effect of hair loss.
In the present, Saitama encounters various monsters and villains, including a rampaging cyborg and a threatening seafolk tribe. Despite his effortless victories, Saitama struggles for recognition from the official Hero Association and the public. He even meets fellow cyborg Genos, who becomes his disciple.