The Nosferatu are a strain of animal hybrid Metahuman. They take on traits of leeches and similar blood-feeding annelids.
While they can look fully human at times, if they are hungry, their form begins to take on a much different tone. They will, when low on blood, begin to secrete a thick mucous layer, reverting to a more annelid state as their eyes retreat into their heads becoming simple light sensing organs instead of visual tools. At this stage, they will rely primarily on touch, taste, sound, and smell to locate targets with highly oxygenated and nutrient-rich blood. A secondary, some consider it a true, mouth will be launched from the humanoid mouth when the starved creature senses prey, latching onto the body to drain blood. They can bend and stretch their bodies in inhuman waysd, having grown additional joints to allow themselves more agile annelid forms when in a hunting frenzy, this provides an added bonus of being able to squeeze through ventilation shafts and similar confined spaces.
While an attack does not spell guaranteed infection for the survivor, it is still recommended to seek medical treatment. Alongside the usual risk for disease associated with both human bites and leech bites, there is also a chance their genetic signature will transfer over in the exchange, presenting risk for a once normal, genetically human individual to begin transforming into a hybridized metahuman. The process begins with the stomach beginning to reject normal food, slowly shifting to a preference for liquid foods, then for liquefied meat products, until a deep craving for any and all blood begins to take hold. It is at this stage that other physical changes begin, the body begins to produce blood that is green-ish rather than red, the bone structure changes to accommodate more powerful muscles, even segmenting in places to allow for more annelid flexibility. Finally, the secondary mouth forms within the esophagus. Once fully mutated, a newly formed Nosferatu will find themselves disgusted by the visage of genetically human people, seeking refuge in other metahuman communities.
Despite having a distaste for the human form, they end up forming remarkably human communities, carrying on as if nothing has changed while they simply live. The advent of medical technology and the positive association humans have with donating blood allows for them to go about collecting blood in fake blood drives without raising suspicion, providing a symbiotic relationship with human, and occasionally metahuman, societies. Due to their intense knowledge of blood, they can smell when someone has a blood-borne illness, allowing them to work as rather skilled and successful hematologists even with minimal training. In a metahuman-friendly area, such as New Ireland, The Russian Exclusionary Zone, or Dark Canada, it is in fact more unusual to simply not employ a Nosferatu as a resident hematologist.
Currently, research is being done on how to synthesize artificial blood that meets the exact nutritional needs of the Nosferatu so they can peacefully integrate fully into human societies. While the underlying principles are understood, the taste factor is currently completely unpalatable for them, and as such extensive trials are being run on deciphering what it takes to make the false blood taste bloody enough. In time, it is likely we can introduce them to metahuman-unfriendly areas as people with a simple blood disease, but for now, we must contend with them being our fellow man despite their separation into the Far Side of this reality.