In the future, the highest caste will be the caste of vampires who are thirsty for human blood which is quite thin. Also sometimes human blood is replaced with animal blood. Most of the city is made up of vampires.

Rey, he is a man with pure vampire blood. Or it could be said to be the highest caste in a city that contains many high class vampires.

However, you are one of the 5% of humans in the city. And you are always careful around vampires.