Hymn Code

The Hymn Code ヒュムネコード (hyumune koodo) is a special identifier owned by each Reyvateil, which serves to register her access permissions and general Cosmosphere settings. Only Origins, Pureblooded β-Types, and γ-Sublimates possess this identifier due to being artificial lifeforms that got their FFT Spectra registered into the Tower's servers right after their creation, while on the other hand, Third Generations don't have them due to not getting their spectra registered at the moment of their awakening to their Reyvateil abilities.

Structure
The Hymn Code is formed by either four or three words, depending on the Reyvateil type the Code's owner is. The structure is as outlined below: So as a couple of examples, we could give the Hymn Code for the Administrator of the First Tower of Ar tonelico: EOLIA_ANSUL_ARTONELICO. From this, it's possible to see that her Name is Eolia, that her Rank is Administrator (ANSUL), and that the SH Server to which she is connected is the ARTONELICO one lodged in the First Tower.

On the other hand, the Hymn Code of a Pureblooded β-Type could be as follows: MISHA_FEHU_EOLIA_ARTONELICO. In this case, her Name would be Misha, her Rank would be "subordinate to Eolia" and her SH Server would be once again Ar tonelico.

Exception - Generic βs
Despite this being the base structure, the Hymn Codes given to the subclass of Reyvateils called Generic βs had the particularity that their FEHU rank contained the entirety of their family history, ending on the β-6D Server they were created from, instead of being subordinated to a Reyvateil Origin (an example of their Hymn Codes being SELLA_FEHU_NANAMI_RX0018J_ARTONELICO). This is because they were connected to other SH Servers instead of the First Tower's ARTONELICO one, and while some had compatibility with it, others didn't have such a compatibility and thus couldn't pass down their legacy when these SH Servers were destroyed during the Grathnode Inferia.

Usage
The Hymn Code is generally utilized for authentication and identification purposes, and with the proper technology, it's possible to find out the exact address in the SH Server for a Reyvateil if her Hymn Code is known. However, their main purpose is for authenticating the Download of the Hymmnos Extracts: the person carrying out the Download must recite the Hymn Code of the target Reyvateil as part of the process, and if they don't know the Reyvateil's Code or if she lacks one, the Download will end in failure.

This is done in part as a sort of safety measure so Reyvateil cannot Download Hymmnos Extracts that exceed the power level they can handle, as otherwise they could exhaust their life force and end up dead while singing the Song. Additionally, the Hymn Codes become unnecessary after the Download of a specific Song has been completed, since they are only used during the Download. However, the Code will still be necessary to Download other Songs into the Reyvateil, and some Songs are even programmed to require a Hymn Code with a specific authorization access in order to be executed.

However, the Codes can also be misused to find out a specific Reyvateil's Soulspace Address and then force a reformatting of her Cosmosphere, instantly killing her off. This is because the Hymn Code, similarly to the Install Port, allow those with the technical knowledge, appropriate software and skill to find out to which Cosmosphere it connects to, which is also a reason why Reyvateils instinctively keep it a secret from anyone they don't trust.

Location
The Hymn Code is created by taking a sample from the Reyvateil's FFT Spectrum, more specifically of the Hymn Code frequency band that is located around 100 Hz near the 116000000 Hz point, which is the area between the Level 9 Cosmosphere and the Shared Consciousness Fields, right after the Boundary Gate that separates the Cosmospheres from each other. The reason why this zone is used is because is extremely stable and not even the strongest feelings can alter its waveform, thus preventing mistakes when it comes to comparing the Reyvateil's Hymn Code with the one recorded by the Tower.

The Codes themselves are stored in a heavily encrypted server called the HNC (Hymn Code Name Server), in which each spectrum sample is assigned the alphanumeric tag containing the Reyvateil's Name, Rank and Terminal Name, with each Code having the possibility of having a duplicate created and getting assigned to a new spectrum sample, as they work similarly to file names in computer systems. Due to its protection, perusing the HNC would require terminals with the proper clearance or specialized hacking to break through the HNC's encryption system.

On the Third Generations Lacking Hymn Codes
While it has been said multiple times that Third Generation Reyvateils don't have Hymn Codes, this isn't strictly true, as they also have the Hymn Code frequency band as part of their Cosmospheres. However, the important distinction to make here is that the Tower doesn't count it for them due to their FFT Spectra not being registered into the HNC's database, while the Hymn Codes for the other Reyvateil types are input directly into the HNC by their creators right after the Reyvateil's Triangular Nuclear Loop is created and put in cultivation inside a Tripolar Resonance Incubator, during which they sample a record part of the Loop's FFT Spectrum. The same isn't true for the Third Generations because they lack D-Cellophanes and Triangular Nuclear Loops, which makes it difficult to record a highly-precise sample of their spectra.

And the reason behind unregistered spectra not being considered by the Tower's systems is that an unregistered FFT Spectrum would end up reading as an incomprehensible mix of numbers, special characters and letters such as "r9cers$3df5%", which can't be pronounced by a potential Downloader and thus would make it impossible to perform Downloads or conduct any kind of vocal authentication. However, around a 10% of the Third Generations end up having these random characters line up to form an actual string that either strongly resembles or is identical to the Hymn Code possessed by another Reyvateil, which makes it possible for them to access to Downloads and gain the same authorization privileges the owner of the original Code had.

The β-ER technique done through the Install of a D-Cellophane works in a similar principle to the above, with the difference being that the Hymn Code frequency band is forced to take an identical waveform to the one possessed by the D-Cellophane's original owner, and said waveform won't revert to its original state even after the D-Cellophane has been removed.

As for the IPDs, while they also have a Hymn Code zone as part of their Cosmospheres, their Spectra isn't registered and thus the Hymn Code goes unused because their Capacity or IPD level is instead the authentication method used for the Downloads of their Hymmnos Extracts. So in other words, they don't make use of the Hymn Code system merely because they don't need it.

Trivia
All the Hymn Code ranks are derived from the names for some of the Elder Futhark runes, which have the following meanings: Ansul means "God", Teiwaz refers to Tyr, the Norse God of victory and war; and Ansul means "property, wealth". However in Ar Ciel, they were coded by the Reyvateils' developers following the Reyvateil format that had been created during the First Era prior to Shurelia's development and creation.