Satoru/Other Media

200 Yen
In his preteens, Mumen Rider attended the same middle school as Saitama. During that time period, he had already begun to act like a hero, calling himself Name-less Bicycle Commuter. He, at one point, attempted to stop two delinquents who attended the school and took people's money. It is later insinuated that he is beaten up by them.

What Can't Be Bought
He appears in the end, taking the drinks Saitama didn't want.

Witness
The Hero Association dispatches Mumen Rider and a group of heroes to defeat Vaccine Man. However, the monster is too strong for them. After Saitama kills the monster, King appears at the scene to retrieve his video game, and the heroes mistake him to be the hero who took down the monster.​

Going Fishing with Middle-Aged Men
Mumen Rider and Chain'n'toad appear tracking down Giant Salamander. They pursue it to a lake, where Kamikaze and Bang happen to be fishing. During the battle, Chain'n'toad is swallowed by the monster, and Giant Salamander begins to taunt Mumen Rider. However, Mumen Rider bravely dives back into action, well aware that he doesn't stand a chance. Soon Kamikaze intervenes, cutting the monster open to release Chain'n'toad and save Mumen Rider. Mumen Rider stands in awe of the S-Class heroes.

Sonic, Becoming Saitama
A monster called Angry Grandpa kidnaps a child. Mumen Rider arrives a delivers a Justice Tackle to free the child and a Justice Punch and Justice Kick followed by a Justice Crane High Kick. Speed-o'-Sound Sonic, who was disguised as Saitama, saves Mumen Rider from a powerful attack and they finish off the monster. Mumen Rider thanks Sonic for his help and Sonic asks why he is a hero since he almost died.

The child gratefully thanks Mumen Rider and Sonic for saving him. Mumen Rider decides to contact the Hero Association to collect the monster. Mumen Rider leaves, suggesting they go drinking sometime.

One Punch Man: A Hero Nobody Knows
Mumen Rider is a playable character in the video game, One Punch Man: A Hero Nobody Knows.