G5 is a large cybernetic robot that bears resemblance to a samurai. It wears shiny metallic armor with long shoulder-pads and spiked claws on its forearms. Its face is covered by a mask with a slit that reveals a single eye in the center.
G5 has a straightforward yet secretive personality. It only speaks when it has a question or when the situation is appropriate. It appears to mind his own business unless it wants to add his thoughts that would be beneficial to the situation.
As a robot, it thinks rationally and not impulsively. It offers his idea of using Narinki's mercenary group as an advantage for the Monster Association instead of killing them.
It seems to have some intolerance towards some of the monsters. He questioned Gyoro Gyoro if monsters could kill one another, focusing on Royal Ripper's murderous attitude towards his supposed allies.
It also seems to be very prideful and confident, as it believed it could defeat Atomic Samurai after copying his techniques.
Human Monster SagaEdit
Monster Association ArcEdit
On its way to join the Monster Association on behalf of the Organization, G5 coincidentally runs into Narinki's Private Squad and captures them, bringing them to the Monster Association. When questioned about who he was by Gyoro Gyoro, G5 tells her that The Organization had sent it to join the Monster Association, probably to help them bring the Hero Association down. When Gyoro Gyoro asks him what The Organization is, G5 keeps quiet.
As the Monster Association are deciding what to do with the mercenaries, G5 steps in and convinces Gyoro Gyoro to use them as their fodder, because of their special battle suits. Gyoro Gyoro agrees and Do-S makes them her love slaves. 
He encounters Royal Ripper and The Great Food Tub as they are arguing over Tareo, promptly grabbing a nearby monster to throw at Great Food Tub's mouth in order to quench his hunger; Royal Ripper notices he is carrying something, which G5 explains is a "hobby of his". The object in question turns out to be the head of the Metal Knight combat unit that followed Elder Centipede on his way back to the monster's hideout; G5 says he kept it because it is "a precious sample" he wants to examine in detail.
After the S-Class heroes invade the Monster Association Headquarters, G5 encounters Child Emperor and Waganma after destroying the former's Radio-Controlled Sentry. He is able to resist the attacks of Child Emperor's Enemy Machine Disabling Device: Bug Kun and swiftly destroy it. G5 battles the newly combined Underdog Man, Mad Dog Underdog Cerberus, while hampered by Child Emperor's bird lime missiles. As G5 battles Mad Dog Underdog Cerberus, Child Emperor and Waganma escape.
Having managed to defeat Underdog Cerberus, G5 comes across Atomic Samurai. G5 fares better than the previous monsters who fought Atomic Samurai, and he is able to exchange several parries. In the end, however, Atomic Samurai is the superior swordsman, and G5 is cut apart by the hero's Atomic Slash. However, the robot inside G5's core manages to escape.
Abilities and PowersEdit
As a Demon-level threat and a "machine god", much like G4, it can be assumed that G5 is a powerful Mysterious Being. It is assumed that he is an upgraded version of his predecessor and thus significantly stronger than it. Additionally, despite only being a Demon-level monster, his design was advanced enough to remain unaffected by Child Emperor's technology, and the hero went so far as to say that it would be a time-consuming effort to defeat him. When fighting against Atomic Samurai, the hero complimented his skills, saying that he would be a good sparring partner for his three disciples, suggesting he is around their level. However, he was still not strong enough to manage against Atomic Samurai's Atomic Slash, with only his core surviving.
Immense Strength: As a Demon-level machine, G5 naturally has impressive strength. He was able to destroy Child Emperor's device with a single swing, and was strong enough to defeat Mad Dog Cerberus without receiving any noticeable damage. In his fight with Atomic Samurai, his swings were strong enough to match Atomic Samurai's, impressing the hero.
Immense Speed: G5 has quick reactions as he was able to rapidly extend his arm to grab a nearby monster and throw it at the Great Food Tub's mouth as a substitute meal. He could briefly keep up with Atomic Samurai in a sword duel, and was able to escape from him once Atomic Samurai destroyed his external body.
- Speed Adjustment: G5 can adjust his speed to better suit his opponent, he utilized his Max Speed against Atomic Samurai in an attempt to overwhelm him, but it was not enough.
Immense Durability: G5 was able to completely negate the effects of a trap device specifically made by Child Emperor to shutdown machines. He was able to defeat Mad Dog Cerberus, one of Child Emperor's most powerful machines, without receiving any noticeable damage. His exterior was obliterated by Atomic Samurai's Atomic Slash, but his interior body remained unharmed.
Technique Mimicry: G5 analyzes his opponent's fighting style and copies their abilities, expanding upon them and improving them. This ability is complimented with his double-jointed limbs, allowing him to perform techniques that usually wouldn't be possible due to the limited range of regular limbs.
Double-Jointed Limbs: G5 has an additional range of motion from his flexible limbs which allows for unconventional angles of attack with his sword. He can also extend his arms several meters.
Simulation and Prediction: G5 can model an opponent's attack and simulate an outcome from the data. However, his simulations can be wrong if his opponent is concealing their true power, as seen with Atomic Samurai.
Laser Beams: His core has the ability to shoot laser beams as a last resort. He attempted to execute Atomic Samurai with a laser beam, but the hero parried the beam with his sword.
Expert Swordsman: While his actual combat prowess is currently unknown, it is likely that G5 is skilled at sword fighting based on it possessing a pair of katanas. He can also copy the fighting styles of others, as was seen with Atomic Samurai. He also stated that he can improve the techniques that he has copied but was still defeated by the hero, so this was likely a boast.
- Flash Attack: Copied from Atomic Samurai by watching his battle with several monsters and Sword Devil Executioner.
- Atomic Slash: Copied from Atomic Samurai by watching his battle with several monsters and Sword Devil Executioner. However, he wasn't able to defeat Atomic Samurai, possibly because the hero wasn't using the fullest extent of his Atomic Slash when fighting the other monsters or G5 simply wasn't fast enough to completely replicate the technique.
Katanas: G5 is equipped with two katanas.
Claws: G5 is also equipped with two claws in his hands.
- ↑ One-Punch Man Manga; Chapter 86, page 9
- ↑ One-Punch Man Manga; Chapter 86, page 8-10
- ↑ One-Punch Man Manga; Chapter 86, page 16-20
- ↑ One-Punch Man Manga; Chapter 89, page 53-56
- ↑ One-Punch Man Manga; Chapter 97, page 32
- ↑ One-Punch Man Manga; Chapter 98, page 9
- ↑ One-Punch Man Manga; Chapter 98, page 8
|Executives||Orochi • Psykos • Gyoro Gyoro • Black Sperm • Evil Natural Water • Homeless Emperor • Fuhrer Ugly • Gums • Overgrown Rover • Nyan • Elder Centipede • Gouketsu|
|Dragon||Gale Wind • Hellfire Flame • Phoenix Man|
|Demon||Awakened Cockroach• Bug God • Devil Long Hair • Do-S • G5 • Hundred-Eyes Octopus • Pureblood • Rafflesidon • Royal Ripper • Senior Centipede • Face Ripper • Fist Fight Djinn • Free Hugger • Rhino Wrestler • The Three Crows • Showerhead • Super Mouse • Unihorn • The Great Food Tub • Vacuuma|
|Tiger||Destrochloridium • Electric Catfish Man • Mad Doctor Fish • Maiko Plasma • Marshall Gorilla • Sludge Jellyfish|
|Unknown||Eyesight • Gyoffrey • Goddess Glasses • Venus Mantrap • Junior Centipede • Haragiri • Rosie • Choze • Benpatsu • Hamukichi • Volten • Evil Eye • Gale • Hellfire • Evil Eggs • Sword Devil Executioner|