Magic and the Towers
The early training for most casters is learning to sense the energies emitted by the Ars Tonelica, and to project their will strongly enough that the tower can sense it in return. This attunement gradually partitions off a section of their consciousness, which is referred to as the songspace. This section of the mind is continually in touch with the nearest Ar Tonelico once it is formed. Once someone has formed a songspace in their mind and casts a spell for the first time, their true name, access level, biometrics, location, and a holographic image of them as they perceive themself is transferred to the Song Server of the tower they cast from.
The access level stored in a mage's songspace determines how much magic they are permitted to draw from a tower every day. Theoretically, if someone were able to hack their own songspace they could modify their access level to draw extremely powerful spells almost at will. However, in spite of extensive research, no method to accomplish this has been discovered (at least, no method that leaves the subject alive). A mage's access level improves over time as they practice and become more experienced.
Choir mage training is a bit unique in that it involves the implantation of a magitech device, called a DH node. This node interfaces with the choir mage's brainstem, forming an additional mental partition called a cosmosphere. This cosmosphere acts as an interface for the choir mages' Songs, allowing the energy to build and channel continuously and to a greater extent than normally possible. The surgery is not without its drawbacks, however. It is possible for a cosmosphere to become corrupted, resulting in many potential disorders or even death. The most common one is called Border Disease, as it affects mainly choir magi who live near the edge of an Ar Tonelico's effective range. The weaker connection results in periodic data loss, which can lead to a buildup of garbage information over time in the cosmosphere. Left untreated, border disease can eventually result in a non-lethal form of dementia similar in presentation to Alzheimer's. Any DH node infection can be cured in its early stages via cosmosphere dive therapy, though this is rather expensive and opens up the choir mage's entire mind to the therapist (so a reputable therapist is a must). However, late stage DH node infections are often untreatable.
Whenever a mage casts a spell in the coverage of a tower they haven't cast in before, their personal data is stored locally in the exact same way as when they cast their first spell, and their access is verified for the level of spell they attempt to cast.
One might think this level of data storage would be both a massive security risk, given the amount of private data stored, and a useful tool for tracking location of a given mage based on where they last cast a spell. However, the only being who can access this information in the Song Server is the Tower Administrator.
A Tower Administrator is a biofluid humanoid construct formed by an Ar Tonelico to act as an overseer of the tower's function and operation. The exact means by which they are created is unknown, but upon the completion and activation of an Ar Tonelico, an Administrator appears at the top of the Rinkernator. A Tower Administrator's personality and appearance varies based on the tower, its construction, the people who built it, and the minds of the surrounding populace. They almost never leave their Ar Tonelico, and should they ever leave the range it covers, they permanently destabilize into their constituent molecules.
Tower Administrators have the last word on whether new spells are accepted into a Song Server, and any newly invented spell will always be stamped with an Administrator's signature. They also can ignore the Tower's normal limits on magic, and can cast any spell or sing any Song at any power level. Finally, they can, at their discretion, cut off any mage from access to the tower, or grant a songspace to anyone who doesn't have one. These abilities make Administrators nearly impossible to overthrow, since they can cast the most powerful spells and deprive their enemies of the ability to cast spells from the Tower entirely.
In the extremely unlikely event a Tower Administrator is destroyed or slain, the tower forms a new one in 1d4 hours. However, during this interval, any sentient being can become the Administrator by accessing the Rinkernator's control panel. The creature must succeed at a DC 35 Will save and a DC 30 Fortitude save or have their brain vaporized by the sudden surge of magic. Should they pass these saves, they become the new Administrator, with the same powers as the previous. Their soul also binds to the Tower, and they suffer the same limitations on travel (as well as the consequences).