In Japanese mythology and fantasy, mazoku (魔族) are supernatural beings, normally evil ones such as devils or demons. A maō (魔王) or maou is a ruler of mazoku, or in fiction more generically a dark lord or powerful monster.
Nouns can be counted. they are the name of a person place or thing. you can also put "the" "a" or "an" in front of them. can you count a "discover" ? can you count a "dark" ? no