A monster named Vaccine Man wreaks havoc in a city and is about to kill a young girl when a bald hero named Saitama intervenes and kills him with a single punch. Saitama recalls the events three years earlier that pushed him to become a hero; after saving a boy with a cleft-chin from Crablante, Saitama resolved to become a hero but became too powerful for his own satisfaction. Following taking out The Brain and Brawn Brothers, one of whom is a mutated giant, Saitama has a dream about a subterranean race who invades the Earth's surface and actually pose a challenge to him, rekindling a passion for battle he had been missing for years. However, when Saitama wakes up, he finds that the real Subterranean race is extremely weak. He kills their leader, and the rest immediately retreat.