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Black Corrosion is a form of Seithr-based phenomena which is corrupted and concentrated. It's produced from within the Boundary by strange sources. Anyone who perishes from it seems to leave a distorted and grotesque formation called the Black Union.

It is a part of the overall Corrosion Anomaly and was a large problem during the The Third War of Ars Magus.


Black Corrosion is the results of being exposed to the deadly Seithr the Corrosion Anomaly is generating. Once contracted, in theory, it's believed that it will drain the user of any strength, and enters the body via exposure of its fine crystal-like form. It seems to play off of the human body which has a small amount of Seithr already inside which it then uses against the victim painfully as it progresses in phases. They experience many unpleasant effects that tear them apart mentally and physically while the effects fill them with more Seithr. These individuals who perish in this manner expel more Seithr from their body, promoting the further spread of itself.

They will become aggressive, and their body will take in Seithr at a high rate, resulting in a Drive being created should they not have one already. Death is very likely should the patient not be able to control their emotions, and reduction to Seithr is common.

Studies of Black Corrosion are mostly kept confidential, so the research on it and its effects is fairly new to the public.  

The Black Union is another oddity of cases of it. Black Unions are found from victims of the Black Corrosion, and it doesn't seem to serve any purpose aside destroying itself but it isn't known how it forms, or if it appears at death or is already inside of the victim. In form, Black Union is a small, black unit of Seithr with a faint red glow to it. It lacks anything and is seemingly hollow. However, they are attracted to souls and the energy of them, meaning they do have some kind of will.

Black Corrosion cases are very rare in the Hierarchical Cities, as its primary agent of the concentrated crystallized Seithr from the Corrosion is blocked off by the powerful Ars barriers which surround the cities themselves.  While Taoreta has the most cases of Black Corrosion due to being a place of exile and lacking the protection of barriers along with being a very Seithr-heavy area with many forms of Seithr carrying the strains of Corrosion. 

In very rare cases, Black Corrosion will turn the victim and their soul into "something else" which is still simply a theory in concept.


It was a prominent problem in the Third War and a problem that the Imperator quickly had to discover how to quell. Unfortunately, this never happened and millions would perish from Black Corrosion to create the Seithr that now infests the current atmosphere.

Black Corrosion was also blamed for the increase of Largely violent individuals and corrupted souls, as well as their Drive capabilities.

Effects and CausesEdit

Black Corrosion progresses through stages.

  • Phase 5: The Seithr inside their body steadily increases the amounts of itself over time gradually making its user more dependent on the Seithr to do any tasks. At this stage, they don't feel anything different, though there may be some mood changes.
  • Phase 4: The flesh begins to merge with the Seithr in black patches that glisten along the area of corruption which can be anywhere besides the heart or soul. The Seithr eats through the flesh and assimilates it into its own form, as the person can begin to lose 'control' over their action and drive.
  • Phase 3: The Seithr begins to afflict the soul itself after it's made it through the bodily defenses, and makes it begin to corrupt and wither away as its sapped of strength. The power within the Soul - 'Drive' is also corrupted as its power spikes and becomes uncontrollable. Should the owner not have a Drive, it will create one on its own. It will often begin to act on its own without its wielder's consent often resulting in episodes of not recalling one's actions, losing memory, or episodes of split personality that manifest in different forms.
  • Phase 2: The mind begins to go. Conscience seeps away, feelings of negativity such as hostility, sorrow, dejection, etc. become present as more and more of the Seithr takes over. The white of the eyes becomes black, and the irises narrow in like a creature.
  • Phase 1: It weakens their soul, draining it of all its power if it had any while their body becomes less and less 'human' as the Seithr tries to take their shape, and the body experiences rejection of this merge as their existence clashes with the changes.
  • Phase 0:The final stage. The Seithr consumes the soul, turning it pitch in a crimson blaze. Everything within the body hits a violent outbreak as they wish only to consume everything but never feel satisfied. A sense of rejection to the process comes over and they begin to decay. The parts of their body that the Seithr was using, break and dissolve into a black murky liquid, until all that's left is a 'Black husk' as their existence itself dies out.
  • Aftermath: A unit of the concentrating Seithr and energy called the Black Union is all that's left behind of the person, the soul will be assimilated immediately. If the Black Union is not contained, it will release a formation of a strange mini beast from the left over 'remains of power', but with little to no power or vitality it finally destroys itself, evaporates in a black puddle, and returns to the Source The process simply repeats in a vicious cycle, as the Black Corrosion will infect a new victim nearby if possible. The Black Union have been taken in the past to be studied, however.


It isn't known what happens when someone survives the stages, there are no records that anyone has, leaving researchers perplexed. Some believe the Black Union and the soul merge, other scientists think it becomes something else entirely. But they do agree a strong soul is needed to survive, one that has been constantly damaged.

It is possible to overcome the effects, some magic has the ability to 'heal' the Black Corrosion or even slow it down. But it can't be stopped permanently unless the unit of Seithr is removed from the body. Unfortunately as of right now there is no way to do so without killing the person in question.

For some reason sometimes the victim will overcome Black Corrosion on their own, this miracle is not yet understood. Such a person is Sylar who exhibits signs of the Black Corrosion, bearing the black sclera and even black patches along his skin, but he is not hindered by it and maintained partial human existence. The fact Sylar generates 'power' goes against the established idea of Black Corrosion only decaying its victims.


Causes of the Black Corrosion are still being studied. There are so far two known causes. 

  • Someone who is exposed to the Boundary directly or to too much Seithr will suffer from Black Corrosion due to the particles of the Seithr from the Corrosion Anomaly being within the Atmosphere.
  • Someone assaulted by the Seithr Being, or a Norai Stigma, will develop Black Corrosion if the wound is not immediately treated and removed of the Seithr.


In Verse 2 it is an idea hinted at many times, with the appearance of Zaezel possibly having something to do with the situations surrounding it. Sylar also very likely has it, due to his black sclera and its one of his motivations for looking for the Azure Sin Subject. 

Black Corrosion will play a large role in Verse 3.



  • All Seithr Beings and Azure Sin Subjects are immune to the Black Corrosion, this is likely because of the fact they're already utterly corrupt beings and may possibly already have it, to begin with. 
  • Nex gains black sclera at command and can switch back at will. Interestingly, however, he doesn't seem to be suffering from any of the stages of Black Corrosion but Sylar's words to him suggest that their cases might be different than others. 

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