Mirror

"Wait!"

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Mirror

The Mirror is a powerful piece of technology invented (or discovered, as he puts it) by Yi Sang and Young-ji. It allows for observation of and communication between Mirror Worlds. Through Mephistopheles, Limbus Company utilizes the device in order to equip different Identities onto Sinners in battle.

The Mirror and the related Glass technology, its abilities, and ramifications are a main point of interest in Limbus Company.

Creation

Glass Window

During one of the League of Nine Littérateurs' illuminators' conferences, Young-ji presented a small device connected to a glass pane, behind which he had positioned a dead chrysalis. Upon activating the device, the chrysalis seen through the glass appeared to revive, with a butterfly climbing out of the carcass. He then explained the technology he'd developed was not equivalent to a resurrection, as the living image was instead overriding the real image, and it would only exist within the confines of the mirror. Young-ji dubbed this creation the Glass Window.
The Glass Window would soon begin to catch the attention of researchers from all over the city, netting Young-ji two official invitations to work for a Wing, although he never disclosed which of them.

Yeonsim

Ever since witnessing the functioning of the Glass Window, Yi Sang was captured by the invention. He recognized some design flaws in it, such as the instability of its frame, and was then encouraged by Young-ji to attempt to recreate it in his own way. Yi Sang thus began the development of a handheld mirror, that would be capable to reflect any possibility without a blur. He would dub this creation Yeonsim, a composite word made of the characters 硏 (to grind or study) and 尋 (to seek).
At a point in time, as the Glass technology had been recognized by T Corp to be extremely useful, the League received a confiscation notice, which would force them to yield their creations to the Wing's Technology Administration Agency. Although many of the League yielded or destroyed their creations with a concept incinerator, Yi Sang was stopped from doing so by Gubo, who took Yi Sang and the mirror with him as he escaped toward N Corp.
During his time at N Corp., Yi Sang, who had already previously found himself enthralled by Yeonsim, as it allowed him to find respite from a daily life in which his inventions appeared to do nothing but take from others, found his mental health worsening due to his prolonged contact with a Mirror World self whose life and abilities he deeply envied, and who seemed to encourage him to preserve the status quo and remain under Gubo's care. The effect of Yeonsim's influence on Yi Sang's mind, throwing him into a deep depression that would last until he was forced to face his past once more in the fathoms of his ego. Later on, during the events of Canto IV, with the encouragement of Dongbaek and Dante, Yi Sang would be reminded of the reason he'd first created the mirror, because of his wish of connection with others, and his wish to continue living. Yi Sang would then decide to change the meaning of Yeonsim's name into 連心, "to connect the heart".

Further Developments

As the Glass technology and the Mirror were both noted to have some weaknesses, such a luck factor related to their reach into Mirror Worlds, more research was warranted. After the fall of the League, the research to improve them both would continue in numerous different settings: Dongrang would attempt to replicate the glass and hand it over to K Corp., which would make use of it to improve the functionality of its Singularity; Yi Sang would continue his development of his mirror under Gubo's direction; the Ring would begin its work on a recreation of the glass, with Aseah as their lead researcher, before he and the Pointillist faction would go on to join N Corp.

Limbus Company

As of the start of 984, a modified version of the Mirror had been installed by Yi Sang and Faust within the engine of Mephistopheles, which would allow the LCB to extract and make use of Identities of the Sinners from other worlds.
Through the use of Mephistopheles' engine, Identities are pulled from countless realities in the form of cards, which must be inserted in Dante's LBC-PDA. The LCB-PDA, connected with the mirror within the engine, is also what allows Dante to communicate with the Identities themselves, who view them and the outside world as if through a glass window. While the overlay may cause unwanted side effects over time, such as headaches or residual traces of the Identity's personality, the system is designed to allow for only a temporary modification of the user's existence and memories, as the overlay will be undone upon separating the chosen reflection from the device.

Hermann's Group

N Corp., particularly Director Hermann's group, has been involved with Glass technology since the fall of the League of Nine, upon which Hermann decided to create a second League, by recruiting Gubo, Yi Sang, and Aseah. Hermann's stated purpose in his research is to find a way to destroy all Mirror Worlds. Hermann's group appears to have continued their work on both Yi Sang's Mirror and Young-ji's Glass technology, the latter of which was overseen by Aseah. Hermann's group does not seem to be currently making personal use of this technology during combat, instead researching it through experimentation and weaponizing their knowledge in pursuing their goals.
Upon acquiring a Golden Bough, presumably the one retrieved during the expedition to L Corp. Branch D-02 in January 984, Hermann decided to make use of the ancient River that flows beneath Wuthering Heights, a source which carries the collective consciousness of humanity, to further her research. Thus Hermann, having previously witnessed Yi Sang's psychological decay, in part due to the Mirror's power in breaking human hearts and shaking the realities of one's existence, made use of the Mirror in her possession to persuade Nelly to switch allegiancies to N Corp., and have Nelly manipulate the ailing Catherine by putting her into contact with countless Mirror Worlds, particularly one that would request to overwrite her. At this point, Hermann could easily convince Catherine to set up a laboratory that would be used for N Corp.'s experiments to create a human "dough", an empty vessel onto which any Identity from a different world might be overlaid. With Linton's complicity in procuring subjects for the research, Hermann began the summoning of an Identity that would wreak havoc across numerous Mirror Worlds, in a process dubbed the Wild Hunt.

The Ring

The Ring has shown active interest in the Glass technology, having taken Aseah from his occupation at N Corp. for the purpose of continuing the research together with Maestro Jumsoon, although Aseah has since been rescued and returned to his work at N Corp.
According to Aseah, the Glass technology is less stable than the Mirror developed by Yi Sang, but is capable of overlaying a larger number of worlds: in fact, the Ring's experiments focused on stacking mutiple realities and Identities into a single person at the same time, a painful experience that resulted in the fracturing of one's mind as it was pulled into different directions. This was defined "Refraction Rate", representing the number of realities being overlaid over the subject.
As revealed in Leviathan, Lapis and Garnet, as well as all the children from the orphanage Vergilius was associated with, were used as subjects for the Ring's experiments with the Glass technology's Refraction Rate. While most of the subjects would shatter or retreat into cocoons, eventually turning into peccatula, Garnet managed to survive the experiment for a short time before being overwhelmed and falling into a cocoon as well. Afterwards, Vergilius would find Lapis, seemingly unharmed and still human, although her original identity appeared to have been permanently overlaid with someone else's, her memories of this reality erased.
The Ring appears to have developed other ways of using Glass technology, such as hallucinogens that take the form of a kaleidoscope, that allow the user to gaze into multiple worlds and experience a sense of euphoria from it.

K Corp.

K Corp. utilizes the Glass technology provided to them by Dongrang to boost its Singularity, the Tearful Thing, and its child entities's production of Tears, by showing the Singularity a continuous feed of violent content.