Genos (ジェノス, Jenosu) is the deuteragonist of One-Punch Man. He is a 19-year-old cyborg and the disciple of Saitama. He is always aiming to become more powerful and fights for justice. Under the Hero Association, he is given the name Demon Cyborg (鬼サイボーグ, Oni Saibōgu) and is the S-Class Rank 14 hero.
Genos has an entirely mechanical body in the model of a handsome young man. His face and ears look like that of a normal human, made of an artificial skin material, and his eyes have black sclera with yellow irises. He has spiky blond hair. His eyebrows are usually portrayed as blond, but in the anime they are brown. He also has pierced ears. Genos wears normal street clothes and sleeveless tops and hoodies in order to allow his arms to transform without hassle. He has been shown to have many different sets of arms, with varying abilities and strengths. Notable examples of his various "arms" are those he used in his sparring match against Saitama and the arms he equipped to combat the meteor. Sometimes the arm sets he uses create a metal framing around his face, like those he used against the meteor and the Deep Sea King.
During his fight against the Forest King, he upgrades his body to have his energy core exposed in his chest and his arms are imbued with a rocket-like engine.
Genos is an extremely serious character. He constantly strives to become stronger and pesters Saitama to train him frequently. Since becoming Saitama's disciple, Genos is very reverent and protective towards his "teacher", although he does express annoyance and disbelief at the mundane training regimen Saitama used to gain his powers.
On most occasions, Genos acts as a comic foil to Saitama's clueless antics, using a variety of special techniques, battle tactics and robotic upgrades to combat villains (and sustaining terrible damage in the process), only to be outclassed by Saitama with a single punch. Due to Saitama's incredible strength, Genos is led to believe that there is a secret to Saitama's power.
Despite their disparity in strength, Genos's diligence earns him greater recognition than his mentor. His superior acumen granted him immediate status as an S-Class Superhero within the Hero Association, compared to Saitama's C-Class designation. He also possesses seemingly vast wealth, enough to repair or upgrade his cyborg body and cover Saitama's rent on a regular basis.
He eventually mellows out, and he recognizes that this is due to Saitama's influence. He eventually comes to respect Saitama not just for his power, but also for his character. This was shown when Genos remarks on how similar Sweet Mask is to Genos's former self when Sweet Mask brutally dispatches a group of alien prisoners with no mercy. Genos slowly becomes less serious and becomes a bit curious about some minor things such as the meaning of fun.
Surprisingly, he is rather disrespectful to those who constantly interrupt Saitama or constantly pester him, as whenever Bang or Fubuki command him or attempt to recruit Saitama, he will continuously tell them to get to the point, and will defend his position as a disciple of Saitama, and nothing else. This hostile behavior does not only extend to those who offend Saitama, but Dr. Kuseno as well. This is seen when Fubuki asks Dr. Kuseno to join the Fubuki Group, he got so far as to call her a "bitch" and says he will incinerate her. Genos will even call out Saitama when he called Dr. Kuseno an old man, but Genos immediately apologized when Saitama told him to give it a rest.
Genos appears to have a certain sense of pride in his abilities and himself. This is seen in his battle against Awakened Cockroach when he shows slight disappointment in having to use the adhesive material, as it would force Genos to accept there were monsters much faster than him. Nevertheless, his fight with Face Ripper, Awakened Cockroach, and Garou demonstrate that he's no longer thinking about raw power and is considering defensive measures. Genos has begun to use tricks to get the upper hand in fights now, although that is usually seen when he has no other choice.
Genos was also a serious person before he became a cyborg.
Abilities and Powers
As an S-Class hero, Genos is undoubtedly a powerful fighter. For someone his age, Genos also has significant battle experience, as he claims to have defeated countless evil entities and organizations before meeting Saitama. His youth and impulsiveness still overcome him on occasion, and he remains much weaker than Saitama. However, despite his amazing growth, he is still unable to fend off against dragon level threats. Fortunately, after his fight with Sonic, Genos has become more open to using tricks to gain the upperhand. His fights with Face Ripper, Awakened Cockroach, and Garou demonstrate that he's no longer thinking about raw power and is considering defensive measures. Virtual Genocide System's (VGS) simulations show Genos (after his G4 upgrade) with > 70% chance of victory against any disaster level demon monster.
Immense Strength: Enhanced by his cyborg physiology, Genos possesses incredible physical strength, and is capable of breaking apart the ground with a drop kick, and punching rapidly with enough force to tear apart a cliff face. During his brief fight with the Deep Sea King, he was able to land a full-force punch on the creature that sent it flying through the roof of the safety shelter. Virtual Genocide System's (VGS) simulations show that Genos can easily beat base form Mosquito Girl in one attack and hydrated Deep Sea King with two attacks after G4 Upgrades.
Immense Speed and Reflexes: He can move so fast that he appears to be teleporting. He was able to keep up with Speed-o'-Sound Sonic for a considerable amount of time during battle. Both of them were faster than sound during their fight.
Immense Endurance: He can continue fighting perfectly well even with only a single arm. With the several battles he has fought, he has been shown to be able to stand on his two feet after several blows from Carnage Kabuto, and he also was still conscious even after he used almost all the energy in his core. However, given the expression on his face after making contact with the Deep Sea King's acid spit, it could be assumed that he feels pain from the direct acidic corrosion of his body. Besides this, he does not often show significant signs of fatigue.
Full-body Cyborg Enhancement: Genos's entire body has been replaced with combat-ready cybernetics and prostheses, giving him an extreme level of strength and speed, as well as advanced sensors and projectile attacks. All his parts have made Genos too heavy to swim and needs special parts in order to do so. Despite these modifictions,Genos is still capble of eating normal food, as shown when he engages in an eating contest with Saitama.
Core (コア, Koa): Genos's cyborg parts are powered by an orb in his chest labeled as the "core," presumably designed by Dr. Kuseno. Genos has shown to be able to put his core into the shoulder of his arm, throwing all of his energy into his heat beams. 
Armor and Replacement Parts: Genos gains not only incredible durability from his armored body, but also benefits from the nature of robotic equipment itself. Genos can lose limbs or have his body torn asunder, only to return to perfect 'health' through replacement parts and repairs (the source of the replacement parts is unclear). As a cyborg, Genos does not seem to feel pain, and can keep fighting even when limbs are severed or he is severely injured. Genos's durability is such that despite taking several powerful blows from Carnage Kabuto and having one of his own powerful blasts reflected at him, he was still conscious and able to stand and walk.
Cyborg Leg (サイボーグレッグ, Saibōgureggu): Genos's legs have a durable design to support high-speed movement. They are equipped with a shock-absorbing mechanism which keeps the interval between landing and the next movement short.
Incineration Cannons (焼却砲, Shōkyaku-hō): Genos's palms contain ports which allow him to fire large and powerful blasts of heat or flame across significant distances. A blast from his palms was powerful enough to obliterate a multistory building which served as the base of House of Evolution. Later, while sparring with Saitama, Genos reveals cannons built into his fists and arms which can produce even stronger blasts. Genos has also been shown to be able to reduce the power of his blasts to a warm breeze, which he uses to dry dishes. During his fight against Forest King, he upgrades his cannons to have a rocket-like engine, which increases the destructive power tremendously to incinerate the Forest King and the entire Forest Tribe with little effort.
Hyper Sensors (ハイパーセンサー, Haipāsensā): Genos's cyborg body contains a number of passive and active sensors which allow him to scan the environment for enemies, both during active combat and while scouting from a distance. The sensors are not perfect, however, as they can still be fooled by the extreme speed of an opponent like Saitama, and their usefulness is still limited by Genos's reaction time.
Search Eye (サーチアイ, Sāchiai): Genos is capable of detecting heat signatures and analyzing speeds.
Adhesive Gel: A tool Genos gained after his fight with Sonic to deal with opponents faster than him. The gel is extremely sticky, preventing fast opponents from moving and allowing Genos to defeat them.
Detachable arms: During his fight with Garou, his hands are upgraded to be able to detach from his body with ease and are armed with rocket boosters to be controlled by Genos remotely. It is also armed with restraining wire to restrain opponents. Debuted after Post-Tournament Upgrade. Genos can also reattach his torso with his body should they be cut apart as seen in his battle with Elder Centipede.Arm-Blade: Genos's arms are armed with razor sharp blades. Debuted after Post-Tournament Upgrade.
Boosters (ブースター, Būsutā): Once engaged, these boosters located in his shoulders enable amazing acceleration and limited flight. Using his palms for jet propulsion in the opposite direction, Genos is able to perform rapid maneuvers.
Arms for Chores: When not in battle, Genos can change into special arms dedicated to house chores. His right hand comes with a built-in vegetable peeler and his palms also allow him to blast a warm breeze to dry dishes. It was also commented that Genos could be the number one housekeeper.
Anti-Saitama Tactical Upgrade: These are a set of replacements Genos used during the National Superhero Registry Arc when Genos and Saitama sparred in the quarry. These arms are differentiated from his normal arms by being black, having much larger shoulders, forearms and fists, and generating a glow between the plates of metal and having his eyes go white when active. The fists and forearms of these arms open to reveal several guns. The beams generated by the guns are significantly larger than his normal blasts and are characterized by smaller individual beams circling the main beam. If he puts both of his fists together the resulting blast is massive, much larger than that of one arm.
Arms Mode (アームズモード, Āmuzu Mōdo): A prototype weapon system that Genos possesses. When inactive it takes the form of a suitcase. To activate it, Genos pushes a button on the handle and then throws it in front of him. The suitcase splits down the middle and separates, each half then opening revealing the "arms" inside with the container then flipping back to become the attaching mechanism. Genos then throws his arms into the new "arms" and they attach to him causing quite a bit of electrical discharge. When the "arms" fully attach, parts run up his shoulders and neck and his face is framed by pieces of metal. The new arms are much thicker and are all black, with the blaster on his palm having changed shape as well. While using these arms, Genos was shown to be able to move his core to the shoulder of his right arm, directing all of his power into a massive blast.
G4 Upgrade: After defeating the battle robot G4, Genos replaces his parts with the parts of G4 which enhanced his speed and power. This enables him to keep up with Speed-o'-Sound Sonic, one of the fastest characters in the series, and even cut off his hair. After this upgrade the design of Genos's arms changes again. His hair also received fiber enhancements to make it resistant to shock, acid, and heat. Moreover, he gained adhesive gel. According to Virtual Genocide System's (VGS) simulations, Genos would be able to defeat the Deep Sea King and Mosquito Girl with relative ease. However, Virtual Genocide System's (VGS) simulations also show that Normal Carnage Kabuto would still beat Genos in two attacks even with the G4 upgrades.
Post-tournament Upgrade: After Genos's body was destroyed by Gouketsu, Dr. Kuseno rebuilds him into a new version that further increases his strength. With these upgrades, he was able to keep up with the "Hero Hunter" Garou who praised his abilities and even compared his physical strength to that of Tanktop Master. Furthermore, Genos can now recall his body parts if they get detached.
Monster Association Arc Upgrade: After Genos's battle against Elder Centipede, Dr. Kuseno fixed Genos up to his new form. This form has sharper, more jagged arms than compared to previous forms. The blaster holes in his hands take the form of a gaping demon mouth and he can fire a blast using both hands in a combined attack. The silhouette of both of his arms form the shape of a dragon. This form focuses on power and lacks balance. Genos can go full-power for around 10 seconds. Any more and his core will give out and explode possibly killing Genos.
Post Psychic Sisters Arc Upgrade: At some point after the final battle with Monster Association Genos received another upgrade from Dr. Kuseno. Genos claims that in this form he has enough firepower to fight dragon-level threats.
Cybernetic Combatant: Genos uses the various inbuilt weapons and mechanisms of his cyborg body to either deliver powerful attacks or to distract his opponents. He is also an extremely skilled fighter in close quarters, able to fight against powerful opponents such as the Deep Sea King for a considerable amount of time with just one arm.
- Incinerate (焼却砲, Shōkyaku-hō): Genos launches a concentrated beam to rapidly heat up a target to the point of being able to melt various metals. It was first used against Mosquito Girl.
- Incinerate Maximum Power (最大出力焼却砲, Saidai Shutsuryoku Shōkyaku-hō): A variation of Incinerate where Genos uses more energy than usual. First used against Saitama.
- Spiral Incinerate (螺旋焼却砲, Rasen Shōkyaku-hō): An improved version of Genos's Incinerate with the upgraded version of Genos's original incineration cannons received after the Super Fight Arc. It was first used against Phoenix Man but is blocked by Elder Centipede. The attack is strong enough to damage Senior Centipede's carapace.
- Ultra Spiral Incinerate (超螺旋焼却砲, Chō Rasen Shōkyaku-hō): A variation of Spiral Incinerate where Genos uses more energy than usual by firing the incinerating blast directly from the core. First used against Elder Centipede. The attack was capable of burning Elder Centipede's insides, although it wasn't sufficient enough to permanently end Elder Centipede's life.
- Self Destruct (自爆, Jibaku): If there is no chance in winning in combat, Genos is capable of destroying himself and his opponent by overheating his core. He first attempted to use it during his fight against Mosquito Girl, but stopped after Saitama interfered.
- Machine Gun Blow (マシンガンブロー, Mashingan Burō): Genos throws a chain of fast punches. It is strong enough to shatter a cliff face. It was first used against Carnage Kabuto.
- Dual Blade Rush (デュアルブレードラッシュ, Dyuaru Burēdo Rasshu): Genos jumps in the air, equips both arm blades and rushes towards the target with rocket boost and proceeds to stab the opponent rapidly. It was first used against Elder Centipede when Genos tried to stab its eyes.
- Boost Attack (ブーストアタツク, Būsuto Atakku): After using his left arm for jet propulsion in the opposite direction, Genos maneuvers towards his opponent and hits them with a strong kick of his left leg. It was first used against the Deep Sea King. Genos uses his boosters to rapidly accelerate towards his opponent to kick them.
- Rocket Punch (ロケットパンチ, Roketto Panchi): Genos's lower arm is retractable due to a cable connected to his elbow, which gives this attack great range. Genos punches at his opponent with extreme force with the aid of boosters inside his lower arm and after the punch, his arm retracts back to its previous state. It was first used against G4.
- Lightning Eye (来航眼, Raikōgan): (Anime-only) Genos uses his eye to produce a blinding flash of light. It was first used against the Deep Sea King.
- High Voltage Fist (ハイボルテジフィスト, Hai Boruteji Fisuto): Genos attacks with a powerful, electricity imbued punch and shocks his opponent with it.
- Rocket Stomp (ロケットストンプ, Roketto Sutonpu): Genos launches himself up with his back boosters and then stomps on his opponent below.
- Lightning Core (雷光核, Raikō Kaku): Genos uses his core to produce a blinding flash of light. It was used during the second sparring match between Saitama and Genos.
- Jet Drive Arrow (ジェットドライブアロー, Jetto Doraibu Arō): Genos uses the rocket boost at full power to deliver the powerful kinetic kick while his leg releases sharp blades at the shape of the arrow head, which is strong enough to break one of Elder Centipede's teeth.
Memo: Genos always carries with him an acid proof memo to write down notes.
- "I am willing to do anything to become more powerful. However, I can't picture myself coming even close to attaining teacher's power"
- (Referring to Sweet Mask) "He reminds me of myself before I met sensei. There is no mercy in his heart. A strong hatred for everything evil, eager to eliminate them all."
- "Using sheer numbers to compensate the lack in strength of each individual, that kind of wishful thinking will get one killed one day."
- "I will eliminate you."
- Genos is ranked 4th in the popularity poll.
- According to the databook:
- What he likes are Saitama's teachings and sardines in oil.
- What he dislikes are people who look down on Saitama and complicated electronics.
- His hobbies are surfing the internet, reading, and writing in his diary.
- Genos is the first new S-Class hero in 2 years however this is contradicted in Weapon where Metal Bat is promoted to S-Class one year ago.
- Genos is ranked #6 in popularity by the public, and is in the Top 5 handsomest heroes.
- Genos as a woman named "Genoko"
- ONE has said that Genos is rather powerful even among the S-Class heroes.
- Genos's tears are made of oil.
- ONE stated a fight between him and Sonic would end in a draw.
- When not in battle, Genos can change into special arms dedicated for house chores:
- His right hand comes with a built-in vegetable peeler.
- The palms also contain ports which allow him to blast warm breeze to dry dishes.
- In an official illustration, a drink bottle opener is built into his right shoulder.
- In the manga's Q&A special, it was commented that Genos (when equipped with 'housework arms') can become a top-class housekeeper.
- In order to become stronger, Genos carries with him extremely detailed "training diaries". A common running gag is that he will immediately scribble down any "words of wisdom" and "training techniques" from Saitama. However, much of the information seems "irrelevant" such as detailed drawings of how to "properly hold and read a manga while slouching on a futon", how to hang laundry on the washing line, and nutritional reports of Saitama's food. Only King seems to realize how useless these wisdom are.
- Genos cut off his sleeves because his shoulders can't fit in them. He also thinks that they are ugly so he cuts them off. Furthermore, he thinks that it is troublesome when he is using his weapons set in his arms.
- Genos got his piercings after he became a cyborg.
- Genos is too heavy to swim under normal circumstances.
- During a stream, Murata drew a Genos-Cinderella alternative universe, featuring Genos as "Deshiderella" (弟子デレラ, Deshi derera) and Saitama as the Prince, with the quote “I’m a Prince for a hobby!”. The other characters were, King as The King, Tatsumaki as The Stepmother, Sonic and Fubuki as The Stepsisters, and Dr. Kuseno as The Fairy God Mother.
- In Murata's stream when describing what ethnicity the characters would be in the real world Murata stated Genos looks German.
- Niconico interview with ONE (Japanese)