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
He was one of the heroes sent to fight Vaccine Man and was defeated. He witnesses what he believed to be King killing the monster.

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.