Genos is Saitama's disciple, he wishes to become strong
Up until the age of Fifteen, Genos was a normal young man who lived with his family. This ended when a deranged cyborg attacked his town, killing most of its inhabitants, including Genos' parents. He was subsequently found and saved by a virtuous scientist named Dr. Stench who had been pursuing the renegade scientist. Wishing to put an end to the creature that cost him so much, Genos begged the scientist to turn him into a cyborg. Stench complied, and Genos has spent the succeeding four years seeking the cyborg. Having witnessed Saitama's awesome physical prowess, Genos asked to become his disciple, hoping that by learning the secret of the bald hero's strength he might acquire the might to avenge his family.
The mangaka "ONE" created Genos for his webcomic One-Punch Man in 2009. In 2012, ONE was approached by Yusuke Murata to consider a collaboration between the two, and the One-Punch Man remake, which also features Genos, was the result.
Genos is a fair-haired and good-looking young man with yellow irises and black sclera.Most of his body appears to be robotic, and while he usually wears common casual clothes like hoodies and jeans, he often leave his metal arms bare.
Genos is a very serious-minded person, very driven, and focused on avenging his family and fighting evil. In many ways he could be seen as an idea hero - selfless, brave, modest and with a strong sense of justice.
Since moving in with Saitama, he has grown quite devoted to him, and has a tendency to hero-worship him, and can become quite angry when he feels that his reluctant teacher isn't shown the respect he deserves.
Genos enters a fight against Mosquito Girl. He kills many of her mosquitoes. Genos then fires a blast at her, but she easily dodges his attack and dives at him, taking his arm in the process, but in return he takes out both her legs below the knees. However, Mosquito orders her mosquitoes to give her all of their blood, transform in the process. She then defeats him. Genos then gets rescued by Saitama who easily defeats the foe. Seeing how easily Saitama defeated her, Genos demands to become his student. A week later Genos shows up at Saitama's apartment, having been fully rebuilt, to discuss being Saitama's student. Genos rather long windily begins to tell Saitama about his past, but Saitama tells him to come back when he can sum his story up with a max of ten words. Some time after, Genos simply asks Saitama to teach him to become strong like him. Later at the house of evolution, Genos enters the battle against Asura Rhino. However he is beaten once again and once again he gets rescued by Saitama who again easily beats the foe.
Genos and Saitama sign up at the 6th official superhero certification exam center. After he finishes the physical and written exam, he is greeted by Saitama in the changing rooms. They agree on how both tests were super easy and that they'll probably get full points too. A hour later, they receive their scores, revealing that Genos received a perfect 100 and is certified as a S-Class hero. Saitama however barely ranks in C class because of his written test. Genos & Saitama later enter a sparring match. They continue the fight, in hoping that he will discover insights of Saitama's power, however Saitama shows impressive fighting prowess and lunges a punch to Genos, but instead flicks him.
Genos receives a call to go to the The Heroes Association for unknown reasons. When he arrives at Z-City branch, with a suitcase, he is greeted by the third-ranked S-Class superhero Bang, who reveals that the Hero Association ordered a mass evacuation and that he and Genos are the only S-Class heroes who showed up to prevent the disaster. He explains that they were given an impossible task, a Dragon-Class Disaster is coming to Z-City in the form of a giant meteor. Genos then gets to the place where the meteor was about to crash. Genos activated his "Arms Mode" suitcase and throws it in the air, forming it into a pair of arms and attaches to himself. As he prepares to blast the meteor S-Class hero called Bofoy flies above him towards the point of arrival of the meteor. Genos then starts to prepare, but starts to doubt his abilities when Bang shows up and calms him down. He tells Bang to get down and then launches a massive attack at the meteor. His attack does nothing to the meteor unfortunately and Genos runs out of power and collapses on the roof. Saitama then shows up and destroys the meteor.
Genos gets a call that J-City is under attack and there was no competent heroes nearby to help. Genos then heads to the J-City to face the Sea king. He engages in a battle with the monster. He ultimately falls against the monster, however Saitama arrives and kills it off.
Genos & Saitama are invited to the S-Class meeting. Then the army of Lord Boros attacks the city. While Saitama goes to the space ship, Genos stays on the ground with other Heroes to protect the city.
When King ran away from G4, Genos stayed to fight King's fight. Genos gains an upper hand, when suddenly a smaller robot got out of G4. G4 then proceeds to overpower Genos. Genos once again gains the upper hand when he throws a fire extinguisher at G4. Genos then states how in the steam G4's laser cannon won't focus because of the steam. Then he states that he knows someone even more powerful than King. And more importantly he states how he is stronger than G4. He then finishes it off. He later visits Dr Stench's laboratory. Genos then tells Dr Stench that he wants to become stronger.
Genos has a powerful cyborg body with many devices built into it. This grants him considerable physical strength, speed and especially endurance, as well as an impressive array of weaponry including lasers and flamethrowers. He is also an intelligent, clear-thinking individual with excellent fighting skills. All of this would seem to make Genos an incredibly formidable and successful hero, however, he is very often defeated, very badly injured into the bargain, and needs his mentor Saitama to bail him out.
Fortunately for Genos, he finds his cyborg body easy to maintain and repair.