A succubus (サキュバス) is a member of the succubi, also called Mumazoku (夢魔族, dream demon tribe). The succubi, a female exclusive race, are one of the ancient races and one of the most endangered. They are on the verge of extinction since, although they can mate with all other races, in most cases the child will not have any succubus trait and only rarely a pure-blooded succubus will be born. The original male counterpart of the succubus, the incubus, has long since vanished from Álfheimr, making it harder to sustain the race.
All succubi have an all encompassing love for all people regardless of race, age or gender, which is what makes them ideal leaders for the Kingdom of Ygvar. They can procreate with all other races, although they can only give birth to females, although only occasionally one of the children could be a succubus, a factor on the decline, the apparition of recessive genes and almost extinction of the succubus race. It appears that mating with incubus was how they were more prosperous in the past and could possible be the reason why Asuha, the daughter of a succubus and a human of incubus descent, retains the succubi abilities without having their weakness.
The progress of the apparition of their secondary sex characteristics happens very quickly, fully maturing in half a year. The first change is the growth of wings, equivalent to a human woman first period, and afterwards other physical changes, such as breast growth, quickly develop.
When they start manifesting her secondary sex characteristics, succubi need to consume sperm regularly in order to keep their vitality and health. In their childhood, succubi drink milk as a substitute.