Vampire

Overview
Vampires have existed fairly unknown by humanity for thousands of years, since Gaius  first broke through the dimensional walls and merged with the body of a human. One of the consequences of this act was that it forever weakened the walls, allowing demons to rarely enter our world when they found a weak point (They can also do this through possession of humans, though they are not actually in our world and don't have access to their true power).

Hell/Demon dimensions had existed for billions of years, since the very first time the First Evil was able to corrupt a normal soul (The only time it was able to corrupt a Transcendial soul was Lilith ) When the First corrupts a normal soul it becomes what is known as a pure demon (While not nearly as powerful as a Transcendial they have been around for far longer (due to the first transcendial soul being less then a Million years old(Lilith)).

Some of these pure demons were so powerful that they used their strength to create their own worlds, their own dimensions outside of our own. They then began creating more of their kind (though these were not nearly as powerful) and would sometimes even wage vicious wars against each other.

When Gaius ripped into our world from the celestial plane it was the first time the dimensional walls had been breached and several lesser demons found their way here, one of which being a blood drinking variety which mixed its power with that of a human, creating the first Vampire or "Half-Breed Demon". The dimensional walls would eventually be unintentionally weakened even more when Baskervilles would later do the same as Gaius, which is why so many more demons/weird shit begins happening once Cain is given his abilities.

Vampires are very similar to those seen in movies such as Blade or Underworld in terms of power, behavior, weaknesses and appearance. The longer a Vampire has been alive the more powerful it becomes. 

They tend to be around 6-10 times stronger then a human athlete, but this power can grow significantly with age. Vampires drink blood, which not only is necessary to sustain them but also gives them a high and increases their strength for a short time. Vampires are allergic to silver, and can also be killed by decapitation and sunlight (One of the main reasons they have tried to remain hidden from Humans). While they have incredible regenerative abilities if they lose too much blood they will either die or go into a coma-like state. Cain can feed on Vampires but he doesn't like the taste, referring to it as being bitter

Amongst the "Vampire Nation" one of the most successful is a criminal Mafia organization that they control. They use it to gain allegiances with powerful human authority figures and even Gaius (who they largely support) in hopes to one day gain control over the planet. Their leader is Cyrus,  a powerful Vampire elder/mob boss and his son James.

While his father is mostly interested with running things in an orderly way, James is something of a renegade and believes that they have waited in the shadows enough and should stop "wasting time cowering in the dark". He has a strong hatred for humans despite the fact that his mother was one.

<span style="color:rgb(0,0,0);font-family:Verdana,sans-serif;font-size:11.818181991577148px;line-height:normal;">Once Cain was given his powers the Vampires quickly realized how much of a threat he would be (seeing as how Cain seemed to hunt down demons/evil doers) and so they began trying to figure out ways to deal with him.

<span style="color:rgb(0,0,0);font-family:Verdana,sans-serif;font-size:11.818181991577148px;line-height:normal;">Cyrus had been witnessing one of Cain's fights that took place in his city and afterward noticed some small splatters of blood that Cain had lost. In curiosity he bent down and tasted it and was shocked to find it made him feel stronger then he had ever felt before. He had his men bring back the sample and told his most brilliant scientists to find out how to synthetically produce more of it (as its not very easy to get the REAL thing from Cain himself). <span style="color:rgb(0,0,0);font-family:Verdana,sans-serif;font-size:11.818181991577148px;line-height:normal;"> <span style="color:rgb(0,0,0);font-family:Verdana,sans-serif;font-size:11.818181991577148px;line-height:normal;">

<span style="color:rgb(0,0,0);font-family:Verdana,sans-serif;font-size:11.818181991577148px;line-height:normal;">Because Cain's blood was a combination of human and Transcendial there was virtually no way to replicate it, but in the end they were able to make a serum similar to it by combining the small sample of his blood with the DNA of various animals, Vampires and Demons. <span style="color:rgb(0,0,0);font-family:Verdana,sans-serif;font-size:11.818181991577148px;line-height:normal;">

<span style="color:rgb(0,0,0);font-family:Verdana,sans-serif;font-size:11.818181991577148px;line-height:normal;">They injected some of Cyrus's men and sent them to kill Cain and retrieve his corpse. While they were far more powerful then before they still proved incapable of such a feat. James even injected himself but kept getting beaten. Eventually he became so infuriated with his continued failure that he overdosed (the serum had only been tested in small quantities) turning his eyes black (The picture above) and greatly improving his strength to the point that he could actually stand up to Cain. The downside of this was that towards the end of their final fight he began to lose control over himself and was seemingly defeated, his body falling into the harbor and disappearing below the waves.

<span style="color:rgb(0,0,0);font-family:Verdana,sans-serif;font-size:11.818181991577148px;line-height:normal;">In reality the infusion would eventually revive him. No longer a Vampire but something more, James would return much later but give up his criminal ways and move to Tokyo where he would take on a more heroic lifestyle similar to Cain himself.