Foremost is a character's Type, Class, and Threat.
The Darkstalkers series organizes the inhabitants of Makai in a specific class system that reflects their social status and level of power. Type refers to the sort of creature a character is: Morrigan would be a Succubus Type darkstalker, Demitri a Vampire Type, and so on. Class is an alphabetized rating that organizes monsters into a social hierarchy determined by their powers and abilities. Threat is a unique measurement that determines their destructive potential; for instance, even if a darkstalker had the highest class rating, if they didn't want to use their power to cause destruction and mayhem then their threat level would be minimal.
Threat levels for darkstalkers and darkhunters alike, or any creature from the demon world, are rated as either: Low, Minimal, Substantial, Severe, Critical, and Apocalyptic. Entities that were previously dispatched with an Apocalyptic threat level include Pyron and Jedah Dohma. The average darkstalker generally has a Substantial or Severe rating while darkhunters tend to be rated between Minimal and Substantial. By human standards, no darkstalker or darkhunter could ever reach a Low threat level, which is reserved only for creatures confirmed dead or other humans.
The classes are ranked as such, by the inhabitants of Makai:
S Class
They are the only beings qualified to rule over Makai as the reigning demon kings. Belial, the reigning Emperor and leader of the Aensland Clan before Morrigan took over, is classified as an S+ due to his enormous power. The previous rulers were Belial Aensland, Galnan Voshtal, and Jedah Dohma, but Galnan's death and Jedah's disappearance has left two of the ruling seats empty with Morrigan taking responsibility for all of Makai in the mean time.
A Class
These are mainly ranked as nobles, particularly the masters of the noble families. They are currently in a deadlock against each other in order to secure one of the two empty thrones of Makai for themselves.
Look at the Makai Noble Families thread for more specific information.
B+ Class
These creatures are more powerful than the average citizen of Makai and have special abilities. They are the warriors of Makai, counting to roughly 10,000 in number, and are the sorts of creatures that would be called Darkstalkers by the humans. Most of the characters in the game are of this class, excluding special circumstances such as Morrigan, Demitri, and Jedah. Even the so called Darkhunters would qualify for this class; they have to, in order to stand up to any of the Darkstalkers that threaten the mortal world. It is somewhat common for Darkstalkers, or "Makai Warriors", to have some blood connection with one of the noble houses but it is not a requirement.
B Class
When compared to the B+ class, they lack any special abilities and powers. They might be able to use magic, however. Most of the residents of Makai are of this class and still outweigh humans in terms of sheer power and supernatural force. There are roughly 6 million citizens of this class that live in Makai and look up to the noble houses for leadership and guidance. These would better be considered the commonwealth of Makai, and most of them have no blood ties to the nobles at all.
C Class
The slave class of Makai. These are the servants to the higher classes, livestock for the nobles, but their value is still high in some capacity. Without the servants, the economy of Makai would collapse. There are roughly 120 million slaves throughout the land with an untold number of duties. Humans would also be considered equal to this class, due to their sentience and the power of their souls.
D Class
This class contains all of the inferior beasts of Makai who have absolutely no humanoid resemblance. Most of them lack any sort of sentience and are more akin to animals in terms of intelligence, but some beasts can understand language and even form their own societies. In terms of raw power, there are also beasts who are stronger than the those of the B Class. There have been roughly 2000 confirmed beasts who are of B+ Class, including Hannya and Kien. The total number of beasts in Makai is thought to be around 30 billion or higher.
NOTE: the B+ class distinction feels so arbitrary to me, honestly I would be fine just labeling them B Class and moving everything else down a letter grade; commonwealth being C, servants being D, and beasts being E, but let me know what you think. I only have it lined out as such because that's what it officially is according to supplementary Darkstalkers material.