Encyclopedia Entry:
A water elemental born from concentrated “water elements” joined with the “monsters’ magical energy.” They’ve become monsters with a woman’s form. They are monsters that have beautiful bodies that are translucent like the water they are made of, and have a pure, kind heart with a gentle disposition. Normally they dwell near sources of water like lakes and springs, and they never aggressively attack humans.
They form a pact with a man through the act of sexual intercourse. The men who form a covenant with an elemental in this way are called “elementalists.” It is said that they become able to make use of the undine’s power over water. It also is said that the undines stay at the side of the ones who make the covenant like a devoted lover.