Chapter 21

 (巨大隕石, Kyodai Inseki) is the twenty-first chapter of the One-Punch Man manga series.

Part 1
Genos reads out the news that Saitama went from last to the 342th place. Saitama is not impressed by it, and asks what Genos has been doing. Genos explains that he ranked 17th, but 6th in popular votes, much to Saitama's shock. Genos reads, without embarrassment, some commentaries of others about him that wrote their impressions after looking at one picture of him. Despite that, Genos exclaims that he has yet to meet someone as astounding as his teacher, to which Saitama is creeped about it. While they are talking, miles above them near Earth, a giant meteor is on impact route to the planet. Genos is called to go the Heroes Association for some unknown reason. Genos arrives at the Z-City Branch, with a suitcase, where he meets Bang. Genos recognizes Bang as the 3rd ranked S-Class Superhero. Bang explains that everyone from the Hero Association evacuated, as all S-Class heroes were called to go there, and they are the only two remaining. Genos wonders why, which Bang continues to explain that everyone is preoccupied or didn't bother, since they were ordered by the Hero Association for an unreasonable Dragon level disaster task. Bang was ordered to stop the impact of the meteor, which could wipe out Z-City, and by protecting the people from the meteor will make the Hero Association's name rise.

However Bang claims it impossible, and advice Genos to evacuate. Genos still stays and asks if the citizens were informed. Bang explains that half a hour ago, they that tried to estimate the point of impact and will announce an evacuation notice. Despite all that, Bang shows a fearless expression of the coming panic. The alarm signals, and Genos wonders what Bang is going to do. Bang is going to stay and is going to protect his dojo with his Rock-Smashing Water Streaming Fist. As he turns around, he notices Genos already left the building. Above them, The meteor destroys a satellite near orbit, heading closer to the Earth.

Part 2
The warning signal to evacuate loud, shocking the citizens and are left without hope. Genos leaps from rooftops and notes that the meteor will also destroy the outskirts of Z-City. He decides to test his prototype, and activates his suitcase which shows the words "Arms Mode". He throws the suitcase in the air, which forms into a set pair of arms and attaches it to his arms and lands on a rooftop nearby the point of impact. Genos wonders if he can do some damage with his incineration cannons and hopes to protect his teacher. As he prepares himself, a huge robot flies above him towards the point of impact of the meteor.

Part 3
The mechanical robot flies towards a building and lands on it. Genos approaches the robot and wonders if it is "Bofoy".

Part 4
Genos pleads for Bofoy's assistance in destroying the meteor, but Bofoy refuses, stating that the only reason he is there is to test out a new weapon system. Bofoy then goes on to reveal that what Genos is talking to is just a remote controlled robot and that his real body is a safe distance away from the imminent impact site and he would rather be called by his hero name "Metal Knight." At that point the meteor roars closer and Genos jumps off to another building he has calculated to be the point of impact, as he is doing this Bofoy lets off a volley of large missiles which hit the meteor, cause a large explosion but doesn't stop the meteor at all.

Genos' mind starts racing about how to destroy the missile when Bang shows up and calms him down. A picture of Saitama runs through Genos' head and he rips his hoodie off and opens his chest plate revealing a 'core' which he then pulls out and attaches into the bicep of his left arm. He then tells Bang to get down and launches a massive attack at the meteor. Genos attack proves to little to stop the meteor and he drains himself of energy and falls to the ground. At this point Saitama shows up and asks Bang to take care of Genos and then promptly launches himself headlong towards the meteor. He quickly arrives at the meteor and punches himself through it, the meteor cracking up and exploding in his wake.

The pieces of the meteor then start to rain on Z-City, destroying a bunch of buildings, including the one Genos and Bang are on. Saitama then lands, looks around, and nonchalantly walks away saying "Well I guess that takes care of it."

Characters in order of appearance

 * 1) Genos
 * 2) Saitama
 * 3) Bang
 * 4) Bofoy

Chapter notes

 * This chapter is the start of the Giant Meteor Arc.