A Latch is a human that has become the secondary body (whether by choice or by force) of a devil. Only certain devils can make a latch, but even in those cases, it can only be done once. Some devils have the ability to make multiple latches (such as Alicia).
Latches can be any human, though some humans are more susceptible to the transformation. The more latches a devil has, the more likely it is that they will cause irreparable brain damage to the Latch. If a Latch is not properly prepared and led through the process, brain damage or death can occur.
No matter the method of infection, a Latch is erased and replaced (killed) once their devil's body is destroyed and their body is needed. They will also work against their own benefit if their devil is in trouble, working only to preserve the body and/or get their devil out of harm's way.
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Most Latches have a blank, empty stare during the initial phases of the infection. Their brain is being rearranged to suit the possibility of a devil needing their body. This usually begins directly after infection if the infection occurred in one Blood Burst. If a devil dies during this beginning phase, the latch is essentially erased and replaced (death for the Latch). This is also the case if the Latch is created while a devil is dying.
Becoming a Latch causes brain damage regardless of the method of infection. The issue becomes how severe the brain damage is. Some situations include:
- Exposure to a devil's blood with no initial contact (Blood Burst, usually from a 'test')
- Constant exposure to the blood of multiple devils
- Direct ingestion of a devil's blood without proper introduction through the skin
- Exposure to a non-latch producing devil's blood over time
- Exposure to a Latch-producing devil's blood during death
The wrong amount of blood can completely wipe a Latch before their body is needed. If this happens before the body of a devil is completely destroyed, the latch is useless. It can also cause the process to become difficult. A Latch may display symptoms of immortality while still being fully mortal, essentially dooming them to death (this usually occurs via starvation - when a latch is unable to eat, mimicking Devil Syndrome, but is still wholly human).
Every Latch will display some symptoms of Devil Syndrome, though these symptoms will prove false if they have been infected improperly OR if the devil cannot produce immortal Latches. A Latch is immortal and will not starve in the transformation process if all these conditions are met:
- Their specific devil causes immortality in any extra body they possess
- They have sufficient exposure to a devil's blood before and after the process
- They are not killed (depending on how they die, a devil can still use their body after death)
Once the Latch has completed the transformation, they can safely exist. As long as their devil counterpart does not have their body completely destroyed (mangled beyond repair or death over 100 times in a small window), they are essentially immortal.
To increase chances of survival, most Latches naturally gain stronger senses. These senses are especially heightened if their devil is in trouble or close to being destroyed. If their devil is too close to complete bodily destruction, the Latch will shut down completely, becoming catatonic.
Latches that are suffering from overexposure to a devil's blood will exhibit strange behavior upon infection. Their senses are heightened to the point of confusion and can lead to risky behaviors. This can cause an overattachment to their devil, even going so far as to smell, taste, and express emotions that their devil is exhibiting.
To encourage the chance of body availability, Latches will become chronically ill if they are away from their devil for too long. This is especially true in cases of blood overexposure before infection. If the Latch is away for too long they can go into stasis to preserve the body.
If their devil is in danger, they can exhibit greater strength than their body can realistically handle, causing damage. They can also be taken over (accidentally) during extreme situations. In these situations, if their devil's initial body regians consciousness in enough time, they will also regain consciousness with some temporary issues.