Satoru/Synopsis

History
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.

Some time after Saitama's victory over Crablante, Mumen Rider applied to the Heroes Association and was placed in C-Class, eventually moving up to Rank 1 for his enthusiastic heroism.

Despite being the C-Class Rank 1 hero, Mumen Rider's motivations for not moving up to B-Class are unknown. Given his claim during his fight against the Deep Sea King that he "wasn't fit to be a B-Class hero", it may be possible that he recognized a personal need to become stronger in order to move into B-Class.

He used to have a license, but lost it after he commited traffic infrigments while trying to stop a crime.

Paradise Group Arc
Mumen Rider helps a small boy by getting his balloon out of a tree. He then rides off to catch up to the Paradise Group. Mumen Rider appears in front of the Paradise Group, when they were causing havoc in the city streets. He introduced himself and says that he will stop them. His appearance seems to reassure the nearby citizens to some extent, however, he is beaten down by the criminal group in an instant. He nonetheless gets the credit for stopping them afterwards, probably due to him being the only hero nearby, when Speed-o'-Sound Sonic and Saitama actually did it.

Sea Monster Arc
Mumen Rider rides towards one of the Seafolk attacking a city, only for Saitama to defeat the monster, before he arrived. He later searches the Heroes Association website looking for information about Saitama, noticing he is close in rank. Mumen Rider was watching TV when he heard of the news about Stinger being at the verge of defeat and rides toward J-City. He later meets with other C-Class heroes telling him that the Tiger threat has risen to Demon threat, but still continues toward the city. Mumen Rider later meets Saitama while waiting for a red light, Saitama goes along with Mumen Rider to where the Seafolk are; however, Saitama decides to leave to go look for Sonic, thinking he was a civilian that took a shower and didn't hear the emergency and was running around naked.

After the Deep Sea King begins his attack on the shelter, Mumen Rider is speaking to the Bearded Worker stating he arrived in J-City. When he is told that the SOS was received from the emergency shelter he immediately picks up his pace using his special Riding-Out-of-the-Saddle Mode, dropping his phone in the process. Upon arrival at the shelter, Mumen Rider attacks the Deep Sea King from behind. The attack appears to do no damage whatsoever to the Deep Sea King, but it quite possibly saved the life of a seriously injured Genos. Despite being heavily outclassed, Mumen Rider proceeds to battle with Sea King. Sea King tosses Mumen Rider to the side and, believing the biker to be defeated, sets his sight back on Genos only to be caught from behind by another desperate attack from Mumen Rider. Assaulted once again by a relentless strike from the Deep Sea King, Mumen Rider refuses to give up, stating that, despite the fact that he is too weak to be a B-Class hero and that nobody is expecting him to win, he will not back down. Encouraged by cheers from the onlooking civilians, Mumen Rider unleashes one final attack that is brutally cut short by an annoyed Deep Sea King. He is, however, saved by Saitama, who compliments him for the fight before fighting Sea King himself. Some time later, after Saitama is promoted to B-Class, Mumen Rider meets him at an oden shop and, revealing that he was the one who sent the single "Thank you" letter that Saitama received, admits to Saitama that a simple note is often not enough, and, also in lieu of celebrating Saitama's promotion, asks the chef to treat Saitama to his best mozuku.

Alien Conquerors Arc
Mumen Rider goes to A-City to help out in the rescuing operation after he rescues a citizen, being joined by Stinger and Lightning Max. The heroes help find and save the civilians that are still in the ruins.

Hero Hunt Arc
Mumen Rider reappears as one of the targets of Garou's hero hunt. Realizing that Garou was an enemy, he attempts to fight him. However, before they can engage in a fight, the Tank Topper Army arrive and stop the attack. However, Garou is again interrupted by Tanktop Master and the two engage in a fight.

During the fight between Tanktop Master and Garou, after Tanktop Master gained the upper hand and was preparing to finish him off, Mumen Rider stops him. Although the other Tanktop brothers disagree with this, Tanktop Master agrees that finishing Garou mercilessly would hurt the Hero's reputation, warning Garou not to come back hero hunting again. After Garou tries to attack again and beats Tanktop Master, Mumen Rider tries to fight him, only to be quickly beaten. At the hospital, he's in the same room as Tanktop Master where he is visited by his friend Saitama, as they discuss whom Garou is, such as that he is indeed a normal human, yet his power is above human and at the same level as those monstrous powers due to a martial arts technique that Silver Fang taught him.

Super Fight Arc
Monsters attack the hospital Tanktop Master and Mumen Rider are staying at. While protecting the patients from the monsters attack, an injured Mumen Rider is nearly killed by Gyoffrey but is saved by Tanktop Master in time.