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This article contains plot details.
Transcendental beings are dangerous to her, as they see the world like she only must know it (a pattern of numbers) and might disturb her control through illusions and qualia, since they can choose to abandon them. In other words, they can discover her true nature and thus be able to confront her unlike any other existence. To prevent this, she has sent Shamshir to hunt all of them down.
She is the primary antagonist of the Epic in that her cycle of prosperity and demise brings doom to all of the protagonists, directly or indirectly, since almost all of them are related to the jewel she is in some way, usually through a weapon they wield. As her reign, through culture itself, is unbreakable, no one is able to defeat her, and the ones who get close to discovering her dangerous nature either die or become her puppets.
In spite of her antagonistic nature, L'erisia is not an evil power but rather force of the universe like any other. Her effects result in what the humans may designate as virtue or vice, but she acts irrespectively of either.
L'erisia is nicknamed "The Crimson Angel", but scarlet actually is not her signature color. Her hair, her eyes, and even her simple, plain dress are light purple (although her eyes are sometimes depicted as being light orange). She has fair skin, and a light build.
Qualia, emotions, meme and culture are as old as humanity itself, if not older. Thus, L'erisia has also been alive for thousands of years, as she is the embodiment of those driving forces of any society.
She herself, under her current form, was, however, born as a consequence of Project Ouroboros, which aimed to grant humanity the eternity it longed for. In order to achieve it, all humans had to give up their memories, their emotions, and basically their whole conscious mind, in order to be condensed into computer programs, which would be stored into a Skyship (the Ark Ouroboros). Joah, one of the scientists involved in Project Ouroboros, was sort of a bug in that structure, could not agree, and released meme into the world again, "reviving" L'erisia, and giving her her current form. Doing this, he proved that humanity could not live without her; his memos contain this story, and are thus protected by L'erisia.
Releasing meme into the world again made the Skyship's algorithm rewrite themselves, "restarting" the Earth, and creating Aria Te'Laria. Humanity's data was spread across the new land, forming the Eight Ancient Races; and as they did not have any memories or qualia, they were just ready for L'erisia to start her reign again.
Zektbach stated that she then proceeds to "manipulate the whole world", since "humans did not even voluntarily go to war, but L'erisia tricked and led them". Her reign goes on for thousands of years.
The opposite force to her cultural and emotional nature is the stable, unchanging and instinctive Nature itself. As a lone Turii child, embodiment of that force, Malchut was bound to encounter her, which she does upon L'erisia calling her. However, unable to defeat L'erisia, she sleeps for over six hundred years, but only to come back as A'milia, The Sealer, the one to end the "curse" of meme over the world and reestablish the reign of Nature.
L'erisia thus finally has to face enemies that can actually fight her, namely, a pure, nature-bound Sealer, A'milia, and two beings freed from her curse : Shamshir, that she had enslaved to hunt transcendental beings, and the reunified transcendental being that is the fusion of the two twins, Matin and Nox, descendants of Lien and thus creations of Sigma. This whole party signifies a victory against Ristaccia's all-powerful and indestructible nature; thus, they can actually battle her, and she has to stand on "equal ground" with them.
Then, the final battle takes place between her and those three. At the end of it, it is said that both L'erisia and A'milia are extremely weakened. The consequences of that fight, that ends the "curse" of self-awareness and reestablishes instinctive nature, reseting the world just like Joah did, are left to be imagined. Zektbach openly asked if defeating Ristaccia actually was the right thing to do.
- Although L'erisia's nature is intentionally ambiguous, despite the fact that she is the antagonist of the Epic, she may have been shown to possess feelings, even if slight, at least for her creator. Indeed, as she was attacked by Malchut in the Raison d'Être PV, it was a flashback of his smiling face that seemingly gave her the force to dodge the offensive.
- The ability of Ristaccia to "magically" give self-awareness, as well as L'erisia's impossibly large power and seemingly impossible existence is explained by the fact that in our world (that previous to Aria Te'Laria), she exists (or existed in the Epic's point of view) in the form of information. This is why she can control anyone, or push men to go to war. It also is the reason why she is often linked to or associated with computers, programs, and binary digits, all of which base themselves on the Theory of Information - hence the name of the discipline they appear in, "informatics".
- Even though the most commonly accepted version is that Joah "woke up" from his unconscious state and decided to revive L'erisia in order for humanity to not stay in that state, Zektbach has stated that this was equally as probable as the reverse. In other words, it is entirely possible that Joah never willingly revived L'erisia, but that she instead managed to alter his data to wake him up and free her entirely. This is an even more plausible order of events, as it explains how he became this "bug in the structure". It is, moreover, supported by the L'erisia PV, which doesn't depict Joah a single time, with the Ouroboros Ark's structures cracking up and being destroyed out of nowhere after L'erisia seemingly wakes up on her own.
- L'erisia can be considered to have a theme song outside of the Epic's work. This theme song is simply named "meme", and was released in REFLEC BEAT limelight, but not in any of the Epic's CDs.