Encyclopedia Entry
A type of centaur that lives deep in forests, etc., distinguished by its beautiful white coat and a single horn coming out of its forehead. Even though it's a monster, it is regarded as "the symbol of purity." It's graceful personality and gentle behavior are that of a chaste maiden.
In the same way as other monsters, they make the man they like their husband and produce children by him; but unlike other monsters, they never attack and force intercourse. The men they become fond of and choose as their husbands are absolutely limited to pure "virgins" who have never had intercourse with other women or monsters. They themselves stay as pure "virgins" and never have sex with any men until they give themselves to their husband. They never give themselves to any man but their husband period. Sex with their man is a sacred act, and the fulfillment of the oath between husband and wife.
Because they possess this sort of nature, they tend to be misunderstood, but just like other centaurs they are extremely lustful. Unicorns without husbands spend their time dreaming of days of sweet pleasure with their husband-to-be. When they swear their oath to their husband, in order to make everything they have dreamed of a reality, they'll use their lewd body they have been saving just for their husband to thoroughly service him. Afterward, they'll frequently seduce their husband and spend sweet days of pleasure continuously having sex just as they dreamed.
There is powerful mamono mana contained in an unicorn's horn, and because of it, they can use powerful healing spells. This healing power grows more potent the purer their "unicorn mana" is. Conversely, if another mana gets mixed in, it loses power. It is said that this is the reason why they avoid men who have had intercourse with other monsters, in order to prevent the power of another monster from mixing with their unicorn mana.
A unicorn's own mamono mana protects against mamono mana from outside, so it normally causes no problems. However, if her husband has sex with another woman, and mamono mana from other monsters accumulates in his body; or if she has sex with a man who has had sex with monsters many times instead of a virgin, then she'll be helpless to prevent it, and mamono mana will be poured inside of her.
When that happens, a unicorn's mana becomes radically distorted and she will transform into a monster called a "bicorn", which, in contrast to the unicorn, is referred to as "the symbol of impurity". They regard indecency as virtue, and desire to live an obscene life even more immersed in pleasure together with their husband. Because of this they'll even call the person their husband had sex with, and then, in order to obtain even deeper, more intense pleasure, they'll have threesomes together.