Episode 4

"The Modern Ninja" is the fourth episode of the One-Punch Man anime series.

Summary
A man named Hammerhead is out to make a utopia of the overworked and underpaid model of modern society. Nobody pays attention to him on the street though, as he announces plans against the rich man Zeniru, who owns a nearby apartment building. Elsewhere, Saitama appears to be having a nightmare about playing "rock, paper, scissors" with someone who has a booger on their finger. Suddenly, he is angered to find out that Hammerhead has made it so that having a bald head makes you dangerous. He runs out to put an end to it.

Meanwhile, Zeniru hires his own bodyguard to protect him against the movements of Hammerhead and his gang. His body guard is named Speed-o'-Sound Sonic. He faces the bald group on their way to Zeniru's lair and warns them that nobody usually survives after facing him in a fight.

In just a few seconds, Sonic beheads just about all of the Hammerhead bald group. Elsewhere, Saitama is getting called a terrorist for his bald head. Finally, only Sonic and Hammerhead remain. Hammerhead manages to escape with his life, but then runs into Saitama in the forest.

Hammerhead prepares to fight him by powering up. Saitama punches his entire suit off, seemingly feeling sympathy for him. Hammerhead runs away naked. Then Sonic shows up and tries to attack him, but Saitama explains that he's not one of Hammerhead's followers. But now that Saitama has blocked his attacks, Sonic still feels he must beat him. Saitama accidentally punches him in the crotch. Sonic then declares that he will train until he can beat him, while he barely stands from that one punch.

Back at home, Saitama tells Genos to leave him alone as he has a serious problem to solve. The problem is: nobody has any idea who Saitama is despite all of his accomplishments. Genos tells him to sign up on the official Hero Register online. Saitama and Genos register together, and must take a hero test to be official heroes.

Trivia

 * King again makes a cameo at the beginning of the episode watching the Paradisers address the public.


 * Hammerhead gives the episode monologue at the end of the credits.