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The «Soul Translator» (ソウル・トランスレーター, Sōru Toransurētā?, abbreviated as STL) is a 4th generation FullDive machine invented by Higa Takeru at Rath. Unlike its predecessors, the machine connects to a human's Fluctlight (consciousness or soul), instead of the brain. As of July 5, 2026, there are six STLs in existence: two at Rath's main office in Roppongi and the other four at the Ocean Turtle.
The Soul Translator’s design is largely based on Koujiro Rinko's design for the medical-use Medicuboid, which in turn was based on the high intensity and output scanner that Kayaba Akihiko used to copy his consciousness onto the Internet permanently at the cost of his life.
The Soul Translator was constructed for the purpose of being used as a method of creating a highly adaptive Artificial Intelligence (AI) to be used for Project Alicization, under the guise of «Maritime Exploration Development». Unlike previous methods of creating such AI, which relied on the use of existing computer architecture for the AI to accumulate experience via simple questions and answers, the AI that is developed for Project Alicization is based on the structure of a human's brain, in order to create an AI with awareness and the adaptability level of a human. As the STL is capable of scanning, and thus copying, the structure of a human's consciousness, called a «Fluctlight», the machine was successfully used in cloning a human's soul and the creation of an AI with the capabilities of a real human.
The basic design of the Soul Translator is rather similar to its predecessor, the Medicuboid, despite the machine being several times larger than it. The Soul Translator is a very large rectangular cuboid machine that, along with the console and cooling equipment, can take up an entire large room, nearly reaching the ceiling at the top. The outside of the machine is not dyed; however, the machine gives off a dark grey-silver glow and mechanical feel due to the aluminium used in its construction. The machine also has a logo of the manufacturer, just the simple words «Soul Translator» in English on its side and a large number on top. Like the Medicuboid, the STL is equipped with a three meter-long gel bed attached, where the user lies down, and a protruding helmet-like interface that completely covers the user's area above the shoulders.
According to the «Quantum Brain Dynamics» theory in the Sword Art Online universe, an «Evanescent Photon» — a light particle that acts as a quantum unit of the mind — exists within the microtubules of a nerve cell. The light particle exists in a state of indeterminism[† 1] and fluctuates according to the probability theory. A collection of these particles — a «Quantum Field» which Rath has dubbed a «Fluctuating Light» (abbreviated as «Fluctlight» (フラクトライト, Furakutoraito?)) — is what comprises the human consciousness, or the human soul.
The Soul Translator is capable of recording the spin and Vecta of each photon within the microtubules and thus translate the information stored within the Fluctlight into a form readable by computers or the other way around - translate the information stored within a computer into a form readable by the Divers.
However, unlike the NerveGear and AmuSphere, the Soul Translator does not use polygons for the 3D models it creates. Instead, the STL uses «Mnemonic Visual Data» (optical memory information) to realize the sensations of the virtual world. The STL maintains and disposes of the Fluclight's five sensory information in the Fluctlight's short-term memory region and inserts new information of what the avatar sees, hears and so forth, creating the illusion of Diving into the virtual world.
Though the Soul Translator operates by manipulating a person's short-term memory, the inserted memories do not necessarily need to be that of the Diver's. As, the Mnemonic Visuals of humans appear to have a common structure, it is possible to insert memories that belong to other people, or are even created from scratch, into a person's Fluctlight, allowing the Diver to experience even things that he or she has never imagined, as well as allowing the designing of worlds that can greatly differ from real life.
The six Soul Translators in existence are connected to a special quantum computer system called the «Light Cube Cluster». A single massive central cube, called the «Main Visualizer», exists within the cluster and stores the extensive Mnemonic Visuals Data of Underworld, allowing all the residents of Underworld to exist within the same memory (virtual world).
The Soul Translator has a unique ability called Fluctlight Acceleration (FLA). As a person’s sense of time is subjective — for example, in a moment of emergency the body produces adrenaline that makes the time flow seem slower for the person, while time seems to fly fast when engaged in a relaxing talk — research was made into how the person's sense of time is controlled by the Fluctlight. It was thus discovered that flowing at the core of the Fluctlight is a pulse that acts as a «Thought Clock Control Signal».
As the brain rarely makes full use of its capacity at processing information during non-critical moments, it is possible to accelerate the thought control signal to handle calculations faster, thus making the flow of time seem slower to the person. During a dream the Fluctlight is sped up to deal with the large amount of memories accumulated over the day, thus making a dream of several minutes feel like it has lasted for several hours. This principle is applied by the Soul Translator, as it is capable of using electric signals to trigger neurons in a way that results in various biological phenomenon that accelerate the Fluctlight's thought control rate, thus accelerating the Fluctlight's sense of time.
However, there an issue arises with the use of such a high Fluctlight Acceleration rate. The Fluctlight has a limited lifespan of its own, estimated to be around 150 years, due to the accumulation of light particle usage for memories. Therefore, when a real human is FullDiving via the Soul Translator, the FLA rate is set to no more than 1,500 for safety measures, while human user is not recommended to spend more than thirty years in accelerated state.
As the Soul Translator renders the virtual world via Mnemonic Visuals, in other words, via memories, instead of polygons, this virtual world is practically indistinguishable from the real world, as every object within the virtual world is at the same level as the real thing in the user's consciousness.
- In the web version, Fluctlight Acceleration was called «Subjective Time Rate Acceleration» (サブジェクティブ・タイムレート・アクセラレーション, Sabujekutibu Taimu Rēto Akuserarēshon?, abbreviated as STRA) .
- A state where actions might happen without apparent causes