A FullDive (フルダイブ, furudaibu) is the technology that immerses the player's senses into a virtual reality. It serves as the technological groundwork for most of the stories in the entire Sword Art Online series.

The system feels realistic enough to fool the mind on a deeper level, and the player's body may react with real responses to imaginary damage, such as spasms or blood pressure peaks. Failsafe protocols and sensor arrays are implemented to keep the player from stress overexertion.

Known FullDive-capable VR Consoles

• At least one arcade cabinet
• NerveGear
• AmuSphere
• AmuSphere 2 (provisional)
• Medicuboid
• Brain Implant Chip
• Soul Translator
• Neuro Linker (Accel World crossover)

2nd Generation

NerveGear

Argus created the NerveGear, a 2nd 2nd generation (1st generation in the Gun Gale Online novel) FullDive gadget. It is a helmet with an internal battery power source that covers a player's whole head and part of face, and it has indicators for power, connection, and one marked "BLK" (that supposedly shows data blocks being transferred). Once worn, it recognizes the player saying "Link Start", and connects to the player's senses by hooking onto the brain to body signalling system and becoming the endpoint for the control signals, as well as providing the virtual reality feedback. It uses microwaves to control the nerves.

When the NerveGear released, it was ahead of its time, and the game makers were not exploiting it to the fullest at first, developing puzzle or education games, walking sims, and so on. The release of Sword Art Online was a much-awaited huge step ahead. Ultimately it was used to trap the ten thousand players online during Sword Art Online's official launch in November 2022. This is also the first FullDive technology to be mass produced.

AmuSphere

The AmuSphere (アミュスフィア amyusufia), which is short for "amusement sphere", is a 2nd generation FullDive system that was co-developed by Yuuki Shōzō's company RCT Progress Inc. FullDive Division led by Sugou Nobuyuki. The system has been modified emphasizing the player's safety. Namely, the AmuSphere's microwave transmitter now has a hard power limit, while various sensors were implemented to continually monitor blood pressure and brain waves and provoke a safety logout feature in case that the player's stress levels put them in danger (Gun Gale Online novels imply that has also been in the NerveGear, and it was possible to opt out). In addition, the AmuSphere allows some of the sensory experience from the real world in, so it would be possible to, for example, shake a player awake, and some players would play in a dedicated isolated room for a purer experience.

3rd Generation

Medicuboid

The Medicuboid (メディキュボイド medikyuboido) is a 3rd generation FullDive system with its primary purpose being healthcare. It was designed by Kōjiro Rinko, who improved on the original machine that Kayaba used to copy his memory online. The Medicuboid is more than just a helmet that overrides the sensory synapses of the user's brain, and also connects to their spinal cord. Its specifications are also much higher than those of a gaming console which increases the effective wetware connection bandwidth and, ultimately, the player's reflex chain speed and reaction time.

The Medicuboid's primary use is not entertainment but allowing people with sensory conditions to have a connection with the real world, as well as acting as anaesthesia, and more. It is achieved by linking their senses to the external sensors, such as cameras and microphones.

4th Generation

Soul Translator

The Soul Translator (ソウル・トランスレーター souru toransurētā), or STL, is a 4th generation FullDive system invented by Higa Takeru at Rath This is the first system that officially bypasses the workaround means like interaction with a player's senses, and instead links to the user's Fluctlight (soul or consciousness) directly. This is based on the hypothesis that the human's self is built on the mix of biological influences and both electric and quantum phenomena as computation means.

Naturally for a system of this level of connection, the STL system features innovative and game-changing capabilities. One of its staple functions, called Fluctlight Acceleration (FLA), is controlling the Thought Clock Control Signal, which is something that is described as not well-researched yet but analogous to the tact impulse generator of a computer's processor unit. That allows the overclocking of the user's synaptic chains in the same way, which in effect habitually decreases up to five thousand times less time to pass in the VR than that in the real world. The STL also puts the world scenes into the player's memories directly, in a dream-like manner, making the mind stop making a critical distinction between the rendered and real worlds.

The STL was targeted for Project Alicization to recreate a human's Fluctlight for use in a highly adaptive artificial intelligence.

Brain Implant Chip

A 4th generation FullDive system that was implemented in Accel World and is mentioned in SAO as being a research-stage technology developed in Santa Clara University. According to Kazuto, the STL gear was way too unwieldy for commercial use, and so the brain implants were the future.

FullDive Non-conformity

As all humans are biologically unique, and interfacing with FullDive gear needs precision, the immersion systems need to be meticulously calibrated and personalized over the course of a first-time connection test routine which takes a while. Even so, some people's physique exceeds the gear's margin of error, and the test may output "FullDive Non-conforming" (フルダイブ不適合). In most of such cases the game would still be playable at a cost of one of the senses being dysfunctional or the experience lagging; however, some people are fully incompatible with commercial-grade FullDive systems.

Trivia

• The NerveGear is mentioned in the Accel World light novel series without the title given. The Accel World TV anime confirms the title in Episode 22.
• In SAO web novel, A NERve Direct Linkage Environment System or NERDLES (ニードルス, Nīdorusu) is used.
• The Augma, an Augmented Reality console that should not have FullDive capability, ends up secretly having it.

References

• FullDive - Fan Wiki