Formally called Moon Cell Automaton.
It is the energy storage device discovered within the Moon.
It is an artifact made by some non-human intelligent lifeforms, and is the super computer used as the setting for Fate/EXTRA.
There are seven layers confirmed so far in its cyber world structure. The first layer, which is the surface of the Moon, is accessible even to run-of-the-mill hackers.
To intrude into the second layer or deeper into the Moon is probably too difficult for non-wizards… or perhaps I should say that there is just no physical way to do so.
Transference of the soul — a body transformed into spiritrons, is necessary to be able to peek any further into the abyss.
Old world magi could connect with the interior portions of Moon Cell as part of meditation without using radio waves.
To put it simply Moon Cell is, “The eye that observes the Earth.”
Moon Cell is a computational device that accurately simulates all of Earth and its life forms, and can even accurately predict the future.
Moon Cell is a database of humanity. A colossal memory device that has recorded mankind’s ecology and history, and even the thoughts and souls of [all] people.
A Pandora’s Box that promises the next stage of evolution, promises god-like power to those intelligent lifeforms who have become technologically advanced enough to scan the interior of the moon.
Originally Moon Cell was just an observation device made by an otherworldly civilization.
Moon Cell only contained equipment to observe and record life on Earth, but after many, many years it came to have its current functionality.
Its mission was to observe, but when trying to observe there can be no “blind spots.”
(Heisenberg’s Uncertainty Principle. The observer determines an event by observing it. What isn’t observed is not certain.)
An observation device must be fair. If it is to observe, there must be nothing unseen. Thus, it required capabilities for knowing everything about the Earth.
To record all things without bias, it needed performance greater than that of an observation device.
And so, it had made a giant leap in evolution.
It had enhanced its functions to the point where it went from making observations to surveilling, even gaining control over the administration of the planet.
The greater its enhancements, the more complex its administration policy. It created many terminals and even made artificial intelligences to manage functions for each section. (These were later utilized for the NPCs and advanced AIs of the Holy Grail War.)
However, on the other hand, Moon Cell was stubbornly opposed to loading artificial intelligence into itself.
A true observer should not have a mind.
If an observer has an intellect and knowledge, the meaning of things observed will be decided by the observer.
For that reason, it kept to maintaining its absolute objectivity as an eye, doing so while always dismantling the emerging semblances of sapience that it had incorporated to administrate its functions.
Thus, this computer has no conception of good and evil, no desire for the future, not even an outcome.
Moon Cell is just a container that exists on the Moon.
A typewriter that God left behind.
An observation lens drilled into the Moon.
In the future, when looking back on this crystal device that just shows people dreams, Moon Cell will be called thus.
The Moon’s Eye.
A bottomless Klein Cube.
The observer of everything on our planet, and a Type-Moon whose master is no longer around.