Numbers

Numbers (数字, Sūji) is an extra chapter of the One-Punch Man manga series included with Volume 10.

Summary
Eyelashes discusses about the factions of the Hero Association and notes that the Blizzard Group is largest and most efficient faction. Eyelashes tries to use this info to convince Saitama to join the group, however, Saitama once again refuses to join. Determined, Fubuki challenges Saitama into a competition where the losers must do whatever the winning team desires. The next day, Saitama comes with Genos, Bang, and King to compete against the Blizzard Group. Before the competition begins, Fubuki asks Saitama to sign a contract, and Saitama does without even reading the conditions. Bang decides to go first, believing that the game will be a sparring match, and asserts that the losers must join his dojo. Unfortunately, the game that Fubuki had in mind was actually a video game, thus Bang was easily defeated. Furthermore the member representing the Blizzard Group, Piko, was a former pro gamer. Following Bang, Genos played the video game, but lost because he did not know how to properly hold a controller without crushing it. After Genos' defeat, Saitama is up next to play the game. Much to Saitama's displeasure, he loses as well. Fubuki, now fairly confident, mocks King, who is the only one left on Saitama's team, stating that it is impossible for her and her team to lose now. King then activates the King Engine and plays the video game. At Y-City, Child Emperor is working on a new invention, "Okame-Chan", which scans the body for muscle mass and the development of nerves, balancing it out with the target's weight to determine the strength of the target's body.

After testing the new invention, a monster alert sounded. Child Emperor, Red Muffler, Darkness Blade, Stinger, and Great Philosopher encounter Jumping Spider. All of the heroes except Child Emperor are easily taken out by the monster. Before Jumping Spider can kill Red Muffler, Bang saves Red Muffler and Genos destroys part of Jumping Spider. Afterwards, Saitama delivers a finishing blow to the monster. When Child Emperor arrives back to the scene the fight was already over. Child Emperor takes the opportunity to measure the strengths of the heroes that have just arrived. When Child Emperor tries to measure Saitama's strength, the invention cracks and calculates his strength as undefined. Child Emperor misinterprets this reading as Saitama being extremely weak. On the other hand, King's strength is also undefined. Fubuki is still depressed that King was able to beat all of her members in a video game. Saitama tries to talk some sense into Fubuki, while the others begin to notice the small spiders on the ground. When Fubuki finally comes back to her senses she crushes all of the spiders with telekinesis. Later on King, Genos, Saitama, and Fubuki all go out to eat at a restaurant called Restaurant Mammoth, with her paying for the meal as per their condition for having beaten her in the earlier contest.