A servamp is a servant vampire, that is meant to serve his eve. A servamp can't die, he only can be "defeated" so far. There is a total amout of 7 servamps and an eighth who the others were not aware of.
Only one person had the power to create the servamps, but it's still a mystery how. He also created Tsubaki in order to eliminate the other seven servamps as he concidered them to be too dangerous.
Most of the vampires are subclass. A subclass always has to obey his creator (servamp). When a human dies or has just died, a servamp must give this person his blood in order to turn him into a subclass/vampire. If a subclass bites a human he won't turn into a vampire - but if the subclass drank enough, the human dies. If a subclass is bitten by a servamp - he/she falls to ashes. Only Tsubakis subclass can be exposed to sunlight, all the others can't.