Mumen Rider is the #1 Class C Hero in the Hero Association. He has a strong sense of justice and will fight all who threaten the peace, even if they outclass him, including the Sea King and Garou. He is one of the few people that acknowledges Saitama's strength, crediting him for beating the Deep Sea King. Although he can move up to Class B, he is very critical of himself, saying he doesn't deserve it. Mumen Rider is a true hero, rushing out to save people during the Boros invasion at the risk of his own life.
Satoru is a young man of average height and weight. He wears an armored suit, with brown armor covering his torso and shoulders. He has a black leather suit under the armor and black gauntlets and knee pads. He also has a green bicycle helmet and dark-shaded goggles. Underneath his helmet and shades, he has short, brown hair and oval-shaped glasses that obscure his eyes.
Satoru is an extremely brave, loyal, and honorable hero who refuses to overlook any crime, no matter how minor or insignificant it may be or back down from any fight, no matter the opponent. He is incredibly determined and never backs down, even at the cost of his own life. He is perfectly willing to give his own life if it means protecting innocent people from evil, even when it is clear he has absolutely no chance of success.
He seems aware that he is weak compared to other heroes, and doesn't feel that he is worthy to move up in class because of it, but he is still more than willing to take on opponents for which the Hero Association sends out for A-Class heroes or above, if only to buy the stronger heroes time to arrive. This shows his selfless concept of self-sacrifice, and how he is willing to go the extra mile, as seen when other C-Class heroes were seen running away from the Deep Sea King.
He is very passionate about justice. He is shown to greatly respect people who save him, as seen when he mails Saitama a letter that he initially tries to compose, but quickly crosses out and finishes with a quick "Thank you!!", afterward asking the owner at the oden bar he was eating at to give Saitama his best serving. Similarly to Saitama, Mumen's heroic deeds are very pure, especially having some sympathy towards villains who seem to have a human heart left in them and appear to be misguided towards a wrong path, such as Bang's former disciple, Garou.
Even though he has been insulted by the Tank Topper Army and several other higher ranking heroes, Mumen doesn't mind. He is also perceptive enough to see what Saitama's true abilities actually are during their first encounter.
He has high expectations of heroes and does not believe they should commit dishonorable deeds. An example of this belief is when he's talking to Charanko in the hospital; when telling Charanko about Saitama and learning of Saitama going to the Super Fight Tournament, he assures Charanko that Saitama would never break the rules to enter in Charanko's place since he is a hero. This could be interpreted as naivety for believing that no heroes can commit selfish deeds.
In many ways, Satoru is a foil to Saitama, Satoru has none of the perceived strength required to be a superhero, and yet he has the immense drive and willpower to be one, while Saitama has all the strength he could need to be a hero, but none of the enthusiasm that Satoru has.
Abilities and Powers
Being the top-ranked C-Class hero Satoru is eligible to be promoted to the B-Class, however, he has refused a promotion because of his belief that he is not strong enough to be a B-Class hero and has managed to retain his place at the top of the C-Class for more than half a year.
Enhanced Strength: Satoru was able to hurt Angry Grandpa, a monster resistant to gunfire.
Enhanced Endurance: Despite his injuries and the apparent pain he suffered, Satoru still continued to fight the Deep Sea King, showing a decent amount of endurance. After being hospitalized by Garou, he is seen battling the invading monsters at the hospital despite his injuries.
Enhanced Durability: Satoru withstood an attack from the Deep Sea King, although he was heavily wounded.Satoru also survived having his head smashed into the ground multiple times by Garou. He also took a hit from one of Hammerhead's crew, which caused severe blood loss of his head, but luckily survived. It should be noted that those battle suits can send a car flying with ease.
Justice Tackle (ジャスティスタックル, Jasutisu Takkuru): Satoru tackles his opponent. This attack is effective enough to make Angry Grandpa let go of his hostage.
Justice Punch (ジャスティ殴り, Jasuti Naguri): Satoru punches his opponent. This attack is effective enough to hurt Angry Grandpa.
Justice Kick (ジャスティスキック, Jasutisu Kikku): Satoru kicks his opponent. This attack is effective enough to hurt Angry Grandpa.
Justice Crane High Kick (ジャスティス・クレーンハイキック, Jasutisu Kurēnhaikikku): Satoru kicks his opponent. This attack is effective enough to knock Angry Grandpa down.
Justice Crash (ジャスティスクラッシュ, Jasutisu Kurasshu): Satoru uses "Justice" as a projectile, hurling his bicycle at his opponent.