One day, when the founder deity and her followers were chased off of the human realm, Mitsuko - later known as Feennia - gathered her loyal supporters and other magical creatures and moved with them to a newly created dimension. A land just for them, for all the magical creatures in need for shelter from the fearsome humans.
After Feennia shared her power with her followers, they turned into fairies.
Some time later her uncle tempted some of those first generationers of fairies and with successfully corrupting them, making them into fallen ones, the first generation of vampires were born. They're the main rulers of this dimension: the fairies and the vampires. Sun and Moon, Light and Shadow.