The ability is called Immune System and it functions through the combination of Transmutation and Emission. The user transmutes their aura to mimic the precise biological functions of antibodies and white blood cells, creating an external immune system that exists outside their body. This transformed aura is projected outward using Emission, allowing it to interact with foreign Nen effects at a distance. When the ability is activated, the user's aura appears as a red and white gaseous substance, though they almost always shroud this visual effect using In so that opponents remain unaware that the ability is in operation.

The primary function of Immune System is to resist and dismantle other Nen techniques and abilities. When the user's aura encounters a foreign Nen effect, it instinctively attaches itself to that foreign aura and begins a process of labeling and analysis. The transmuted aura reads the unique signature of the ability, examining the flow of aura, the category of Nen being used, and the specific intent that holds the technique together. Once this labeling phase is complete, the user's aura begins reverse engineering the foreign Nen effect by identifying the structural knots that maintain its form and applying opposing aura waves to unwind them. This process turns the complex and structured Nen ability back into raw, neutral aura that dissipates harmlessly into the environment, wasting the target's aura in the process. The reverse engineering takes time that varies according to the complexity of the outsider's Nen effect, with simple abilities requiring only seconds while extremely complex or abstract techniques may take mjnutes to fully dismantle.

Once the user's aura successfully defeats a specific Nen effect, the method for reverse engineering that technique is saved within their aura. This means that subsequent encounters with the exact same ability require only a few seconds or even milliseconds to neutralize, making the user increasingly dangerous against opponents they have faced before. However, this memory function has a finite capacity, and the user can only store a limited number of blueprints within their aura at any given time. If they wish to memorize a new technique, they must overwrite an older one, effectively forgetting how to counter that previous ability. The limit isn't artifical and depends on the user's own mental capacity, the complexity of the method, and nen mastery.


The ability is not intended to combat aura that is used in basic universal ways. Techniques like Ten, Ren, Gyo, Ko, Ken, and Ryu cannot be reverse engineered because they lack the complex structure of a unique Nen ability. Against these basic attacks, the user relies on a secondary defensive mechanism that functions like a lizard shedding its tail. They project a layer of their aura onto the incoming raw attack and allow it to stick to the foreign aura. At the moment of impact, the user emits that stuck portion of their aura, peeling it away from their body along with the kinetic force or damaging energy of the attack. This reduces the damage they take from basic Nen assaults without requiring them to reverse engineer something that has no complex structure to unravel.

The user can only use Immune System to protect themselves, and it has no effect on Nen effects that target other people, their aura simply will not engage with foreign Nen that is not directed at them. This limitation is absolute and cannot be circumvented through clever interpretation. However, in vague situations where it is unclear who the actual target of an ability is, the user is permitted to protect themselves. This is the only circumstance where the user could potentially help another person, though the help would be indirect at best. For example, if a wide area ability is released and it is ambiguous whether the user is among the intended victims, they can activate Immune System to defend themselves. If their defensive aura happens to intercept or disrupt the ability in a way that also protects someone standing nearby, that is an acceptable side effect, but the user cannot deliberately aim to shield others. Their intent must always be focused on their own defense, and any benefit to others must be incidental rather than intentional.

The user remains vulnerable during the analysis phase of a new ability because a significant portion of their aura is committed to the reverse engineering process. This leaves them with less aura available for basic defensive techniques like Ken or Ryu, making them physically more susceptible to brute force attacks during that window.