Beast Vassals or familiars are beasts in the form of sentient, ultradense magical energy brought from another world via blood flowing through a vampire's veins. Their abilities and forms vary according to the host. As Beast Vassals consume the life force of their host when they materialize, only vampires, who have an infinite "negative" life force, can employ them.
While Beast Vassals have varying strengths, even the weakest among them surpassed the power of an attack helicopter or a state-of-the-art main battle tank. It was said that the Beast Vassals employed by Elder vampires were capable of blowing away entire villages. Once released, there was no way to stop a Beast Vassal except by smashing it with an even more powerful magical force.
There were numerous demon races that matched vampires in brute strength, agility, and innate special powers. However, the existence of Beast Vassals made vampires even more fearsome, making them the "Lords of Demonkind". Even experienced Attack Mages feared vampires. Most vampires are able to summon a Beast Vassal. Powerful vampires, such as Primogenitors, are capable of summoning multiple Beast Vassals.the son of Satan was said to be the top familiar currently located within the first primogenitor or Lost warlord.