Volume 4

"Giant Meteor" (巨大隕石, Kyodai Inseki) is the fourth volume of the One-Punch Man manga series.

Summary
A single man arose to face the evil threatening humankind!

His name was Saitama. He became a hero for fun.

Saitama went with Genos to take the professional hero exam and passed with flying colors on his first try! Now he begins his service as a new Class-C hero.

But he wasn't aware of his quota of one heroic deed per week, so he is suddenly faced with the crisis of losing his registration! As he races around town looking for trouble, he runs into Speed-o'-Sound Sonic. Sonic wrecks havoc on the city, and Saitama defeats him, but...

Trivia

 * Black Sperm makes a cameo in the volume.