Yin and Yang

Yinari (black) and Yanira (white) are a pair of dancing fox spirits known by many a summoner, for their dances hold fearsome power in combat. Despite being close friends and later lovers for many long years, they have been torn apart many a time, being summoned one at a time by different masters (the ability to summon even one of them a great feat for a summoner) and even made to fight each other a few times. Imagine their surprise when they came across a master who was not only able to summon both of them to her at once, but also have the energy to keep them both bound to her as her familiars for the rest of her long life as a kitsune. Not that they terribly mind, as she takes good care of them both and they can be together without interruptions. Even if they have to do a lot of things for her.