Xeiran Host

Transmission & Vectors

For the sentient Xeiran to actually enter the body, the consciousness gradient must enter on some opening on a human—this can be through an open wound or something like a mouth or eye. The most effective transmission is through an open wound. The xeiran must also be injured with a bleeding wound. This means that the Xeiran will bleed into the human. The human will either begin to integrate to the xeiris and accept the xeiran, or it will reject it. This doesn't always spell instant death for the human, but it's not pleasant either and can result in death if immediate attention is not given. Basically rejection hurts. 
Sentient Xeirans are typically artificially implanted to create sentries (Hypnosis). Sometimes the mind suppression is unsuccessful so you have two fully conscious entities occupying one physical body. This is typically how conscious hosts are created. 
Accidental implantation is an occurrence, but it typically never happens just because it's so rare. (It has happened, though. The second recorded Host was an accidental implantation)

Symptoms

Very dependent. Many different things can happen depending on several factors, including the consciousness of the human host and Xeiran, the relationship of the human and Xeiran, as well as the acceptance rate.
Common Symptoms: (when accepted)

High amounts of xeiris in the bloodstream.

Black line-like markings originating from the entry point.

Some or all of their hair turns white/silver.

Varying ability in controlling or producing Xeiris.

Increased metabolism and appetite.

Increased physical capability (strength, stamina, speed, etc.) 

Sclera possibly turning black (not permanent)

Eyes are suddenly a bright fuschia. 

Conscious Host:

Hearing only one other voice.

Seeing the reflection of someone else (the appearance must be consistent, but it doesn't have to happen every time the human looks at a mirror)

Sudden physical change. (Possibly on command)

There must be a lot of alternatives that have to be eliminated in the event of being a host because conscious hosts experience psychosis-like symptoms due to having the Xeiran's consciousness also being present.
Unconscious Host and Xeiran:

Despite appearing alert, there is only minimal consciousness.

Responsive to physical stimuli but cannot answer questions regarding the individual.

Typically only speaks monosyllabically, and only in response to simple questions or orders.

Loss of individuality and awareness of self.

Robotic, lack of emotion. 

Appearance can vary. Either a combination of the human and Xeiran's appearance or purely the human's original appearance.

Further research shows that hosts are able to identify other hosts because of the xeiris nexus.

Treatment

Currently untreatable. There are very few hosts that VANGUARD can actually research, limited to mainly only Rien Occulus and Omni Galoin.
The xeiran and human can be split with the Sword of Unity and Separation, but you gotta stab yourself with it. This effect is not yet known.

Prognosis

The long-term effects of being a host are unconfirmed because there's very limited information on it since it's a very new condition.
VANGUARD regularly does tests on Rien to monitor the effects since he's the longest recorded host, however, it's only been 12 years. So far he's showed no signs of any decline in health. He constantly looks sleep deprived and scruffy, but that could solely be a reflection of his lifestyle. Not enough information is known for any proper conclusions to be drawn.

Affected Groups

Anyone has the potential to be a host. It only comes down to whether the human body will accept the xeiris. At that stage, your fate is entirely up to RNGesus. Researchers haven't been able to find a reason why the xeiris would accept or reject a human.

History

It was first studied by humans beginning 9 years ago when 14-year-old Rien Occulus was found and identified as a survivor of the Fulmina Eruption. It was discovered he had a relatively high concentration of a strange substance in his bloodstream. They centrifuged his blood and found a layer of a strange black and blue substance. It's identified as Xeiris, the true form of Zelvium. Humans have been found to have Zelvium in their blood, but never pure Xeiris. Further analysis was done on him and they found that a Xeiran, Erhea, was inside him.

Cultural Reception

The condition of being a host is unknown to the public, as they aren't aware of the existence of Xeirans. Hosts are incredibly rare anyway, to the point where they're anomalies that have practically no presence in the mind of the public.

Type

Parasitic

Origin

Alien

Cycle

Chronic, Acquired

Rarity

Unique

Affected Species

• Xeiran
• Human