Virtual Genocide Simulation

The VGS (Virtual Genocide System) is a headset designed by Dr. Kuseno. The headset is meant to catalog the data and simulates battles between the wearer and monster data stored in VGS.

Overview
The VGS works by reading the brainwaves of the wearer, and simulates battles between the wearer and monster data stored in VGS. The wearer pictures the scenario and the scene of the fight in their head and VGS will carry it out in the simulation, with the resulting battle is visualized on an external monitor.

Another feature of the VGS is the ability to create ghosts of the user. This is done by downloading the data of the user into the VGS and having the user fight his own ghost with the intention of strengthening the user's abilities. However, the VGS is incapable of registering certain abilities into its system, and it is also heavily affected by the user's thoughts. Examples of this are seen when Metal Bat fights Carnage Kabuto in the virtual simulation, but the battle ends when the VGS deems Metal Bat's injuries too serious to continue, failing to register Metal Bat's fighting spirit. Another example is when Zombieman's body is destroyed, leaving nothing but his head, yet the VHS continues to go on because Zombieman doesn't think his injuries are very grave. When Saitama fights himself from the day before based on the data collected, Saitama defeated him in a single punch. This could signify four things:
 * 1) The VGS is incapable of properly registering and downloading Saitama's true power and thus can't create a proper ghost.
 * 2) Since Saitama had the mindset of being victorious over his past-self, this caused the simulation to be rigged toward Saitama.
 * 3) The data collected by the VGS didn't represent Saitama's true power, and the ghost inserted in the VHS was just a fragment of what Saitama is truly capable of.
 * 4) Saitama truly became more powerful than he was yesterday, although this is the least likely because Saitama believes the data to be unreliable and already had the mindset of victory over his ghost.

Plot
Sometime after Genos' G4 upgrades and before Genos meets Gouketsu, Dr. Kuseno invents the VHS and gives it to Genos. Genos easily defeats all enemies in VGS artificially created by Dr. Kuseno. Once he defeats them, he then his training to the next stage by uploading data collected on monsters he fought and collected data on into the VGS and engaging in simulated battles with them.

Once the simulated battles are finished, Dr. Kuseno advises him to create a ghost of himself by uploading his battle data onto the VGS. Genos does as he says, and he trains diligently with his ghost. After spending some time training with his ghost, Genos wants to see his improvement and aims to test his ghost against Saitama. So he takes the VGS to Saitama's apartment and asks Saitama to test the headset. Saitama is reluctant at first, but he eventually agrees and tests out the VGS.

After Saitama finishes the battle simulations, Genos is disappointed by the anticlimactic results, but realizes that it was naive to think he could understand Saitama's power through a simulation. Meanwhile, Saitama realizes he punched holes through his apartment wall during the simulation and becomes enraged.

Genos wants to get more data and see the VGS work in-depth, so he contacts HA and sent out a call for powerful heroes to gather at the HA headquarters to get more reference data for VGS. Sneck, Metal Bat, Zombieman, and Superalloy Darkshine all agree to test the VGS. The heroes then engage in virtual combat with Carnage Kabuto.

Once all of the heroes finish battling him, Superalloy Darkshine asks Genos if there are any more powerful monsters in the VGS. Genos tells him he could upload a ghost of himself and fight the ghost, and Superalloy does just that. However, he accidentally fights Saitama's ghost and is defeated in a single punch. The VGS breaks, and the heroes believe the device is bugged.

The next day, Genos comes back to Saitama's apartment with the repaired VGS and asks him to do battle with Saitama's ghost from the day before. Saitama agrees, but as he puts on the helmet, Genos begins to panic, believing if Saitama loses to his ghost, he will be affected mentally and decide to quit being a hero. Genos tries to explain to Saitama what he is getting into, but by then, the virtual battle already started. When it is over, Genos consoles him and tells Saitama it is okay to have lost to his ghost, but to the cyborg's shock, Saitama defeated the ghost in one punch. Genos marvels at this, wondering if Saitama became much more powerful than he was yesterday. Saitama tells him it was just unreliable data and goes on a short monologue describing how training in a virtual simulation will not give you any growth, with Genos vigorously taking notes.

Trivia

 * It is said that ONE had spent over 10 hours to make changes/amendment for the script of Genos, Training, basically making it canon material.