Beings who obtained their immortality by consuming others, which has resulted in their ethics concerning life shift drastically. Since they attack living things in a chaotic manner, wildly different from the Diabolus, they have become a major threat to the remaining human race. However, they aren't stupid.
Nosferatu who consume other Nosferatu are known for suddenly mutating, and many such mutations are known for having rational minds, but they still commit various inhumane experiments on humans and other living things.
Though cute animals stand on their side, it would be smart to assume that those creatures have already been turned into part of the Nosferatu. Among even the residents of the Black World, they are detested, as large numbers of them lurk deep within hidden caverns and underground ruins.