Los Viejo-Hueco Mundo Defenses & InformationChūo Seishin no Taihō:
Also known as the "Central Spirit Cannon", this particular defense is Los Viejo's primary way of eliminating invading forces once they're actually inside Hueco Mundo. This device is by far the largest machine on the moon, being nearly as large as a human city by itself. The primary part of it, the cannon itself not the base, is nearly a hundred kilometers tall and one of tallest structures in all of Hueco Mundo. The base, which consists of the buildings where the machine is operated and maintained from, are miles wide. This is because exactly what is necessary to power this massive cannon. In order for this cannon to fire, it must draw in energy from all of Los Viejo, the moon (including the machinery and people on it), and the very air itself in Hueco Mundo.
By absorbing spiritual particles from it's surroundings for hundreds of miles in every direction, this cannon is able to gather so much energy just being near it can cause death to anyone below Captain level while causing extreme damage to those actually on Captain level. This is before the cannon is even ready to fire, which really shows how dangerous this weapon can be. After gathering an amount of spiritual energy seen nearly nowhere else in any realm, the Central Spirit Cannon is ready to fire. At the command of Nagato Tengan and him only, as no one else has permission to use this due to not only it's power but the danger it poses to Los Viejo from the energy gathering process, it will fire. When it fires, every single bit of energy it has absorbed is released in the form of a humongous beam nearly a kilometer wide. This beam is capable of wiping out entire cities in an instant, though that is not it's use. The pure condensed power of this weapon is enough to not only severely damage even 0-2 level beings, but do so even in their release states. It is also extremely effective at wiping out armies in a single go, as large amounts of mooks stand no chance against the cannon's firepower. A good example of what it's capable of doing is Nagato Tengan believes it would be enough to cause tremendous damage even to himself, despite the fact his Hierro is regarded as the strongest. It should also be mentioned that due to the massive volume and volatility of the energy used, it cannot be absorbed or negated by essentially any means without the individual suffering from extreme drawbacks bordering on fatal if they survive.
The issues with using this weapon is it's charge up time, down time, and potential side effects. First, it takes an entire posting round to charge up completely meaning it cannot be used immediately. Second, due to it's power it can only be used once a thread, once a month. That means once it is used in a thread, in cannot be used until a month after the thread ends. If used before this time, it could potentially destroy not only Los Viejo but the Moon as a whole. As for side effects, if the Central Spirit Cannon is used anywhere near a Hueco Mundo city, the city would likely suffer extreme damage or even be totaled completely. This is especially noticeable if the cannon is used and Hueco Mundo forces are nearby, as anything below vice captain level would be eradicated completely from existence within the blast radius. Using the cannon also puts Los Viejo out of commission for a while, and it's pretty much guaranteed the other defenses Los Viejo provides for Hueco Mundo will be cut down to about 5% output and effectiveness.
Matriz Hueco Sistema:
This was a system originally devised for the protection of Los Viejo, and Los Viejo alone. However, Nagato Tengan expanded the Hollow System Array to cover a scale larger than even Earth's surface area in order to encompass as much of Hueco Mundo as possible. The original creation of this system came from the discovery of a Hollow that had the power to send radio waves across long distances. Hypothesizing he could build upon this Hollow's power to support Los Viejo's wavelengths used by it's machinery, Nagato took this creature and artificially essentially recreated it to serve his own purposes. This Hollow now takes the form of a massive pylon over three hundred meters tall located on Los Viejo's moon, as well as over a hundred large, marble-like obelisks floating many kilometers above Hueco Mundo.
How this works is Nagato uses the central pylon to send signals to the floating obelisks to perform specific functions. There are varios functions running at the same time using this system, all of which provide protections of some sort to both Los Viejo and Hueco Mundo as a whole. Both the pylon and the obelisks were constructed to be extremely durable, to the point where likely only captain-class fighters can destroy the obelisks and only people above even those can damage the central pylon. Also, the only real way to collapse this system is to either destroy the central pylon itself, or at least half the obelisks. However even with downed obelisks, this system can still operate (albeit with lower efficacy.
One of the primary uses of the Hollow System Array is a massive sensory field that feeds back data to Los Viejo. This works mainly to detect intruders, invading forces, and generally all those who enter Hueco Mundo without permission. The information sent back to Los Viejo is pretty accurate, and the sensor itself is extremely accurate. It can pick up individuals who are nearly powerless, and their individual information sent back to the pylon includes their general power level, race, gender, and physical characteristics. Los Viejo can then use this information to determine if the individual is enough to be considered a threat, and then dispatch soldiers or higher level warriors depending on the severity of said threat.
The second use of the system is more recent, though just as important (perhaps in less situations though). A specific energy wave invented by Nagato is sent at all times from the pylons to the obelisks with one main use in mind: prevent the intrusion of all foreign energies and dimensional tears. While you might think "Wouldn't this also prevent the use of Garganta, etc?", this was made to allow individual travel into Hueco Mundo (for returning Hollows/Arrancar), and mass travel out (for if Hueco Mundo goes to war). This is primarily geared towards preventing outside forces or energies, no matter their type or makeup, from intruding upon or disrupting the stability of Hueco Mundo itself. This includes unknown signals/energies.
The third and final current use of this signal system is what can happen if war breaks out within the confines of Hueco Mundo. By massively overloading the pylon with energy, the entire system will be overloaded as well. What this allows central command at Los Viejo to do is transfer this energy from the obelisks on a wavelength only Hollows and Arrancar (not Vizards and other 'Hollow-esque' races) can pick up, providing them all with general boosts of power. This means even low level Hollows would pose a threat to, for example, seated Gotei members. Stronger warriors can appreciate this boost even more as it allows middle class fighters to take on captains and above on at least equal footing. Maxed out, all Hollows and Arrancar connected to the system within Hueco Mundo, or those in Nagato's favor, gain access to a tier boost of power (however using this nobody can reach 0-2++ or 0-1). However, doing this can and almost always will temporarily weaken or eliminate the system's other uses.