Hosts are humans with a previously undiscovered viral symbiote present in their cells. They were discovered by Christophe Noircoeur, a graduate student in France, on December 9th, 700 +WT. Hosts require a diet high in electrolytes to support their abilities, and unless they also happen to be weavers as well usually don't realize their abilities. Even amongst Weavers, Hosts are considered to be are incredibly rare as only two have been identified worldwide. This viral symbiote endows Hosts with notable traits primarily related to their nerve cells. In a Host's photoreceptor cells the infection expands the range of the electromagnetic spectrum that a Host can perceive. In almost all of the other nerve cells a Host's axons are widened by 5-10 µm. This results in an increased reaction time and response. In addition to the nervous system enhancements observed in Hosts, the subconscious ability to slightly manipulate gravity when it comes to the effect on a Host's body is also granted by the symbiote by unknown means. This allows a Host to increase his/her own jumping ability as well as protect themselves from otherwise fatal falls, without the use of Madō. It should be noted that this gravitational ability cannot expand to manipulate separate objects or targets that aren't in contact with the user. The final ability of Hosts is that if they happen to also be weavers they are endowed with an enhanced abilities usually that pertain to their natural Madō skills.
Hosts share an appearance and physiology, except the nervous system alterations, with normal humans. The only known feature that is common to hosts is their eyes will be a shade of purple. It should be noted that since the host condition is the result of a human viral infection, Hosts may be limited to the Humans and partial humans. It's unknown if the condition can be passed through blood to blood contact, but it doesn't transfer as an airborne pathogen. It would also seem that the normal Human immune system destroys the Host virus, preventing the symbiotic relationship from occurring. Due to the enhanced state of a Host's nervous system, nerve agents work especially quick, but in turn pass from the system at an increase rate as well.