User blog comment:B214/Question and Answers 6/@comment-26293136-20170319221826/@comment-29963364-20170319232159

The Five Great Families, Nakiri, Shinra, Himejima, Kushihashi, and Doumon each were bestowed one of the Five Sacred Beasts by the Shinto Gods.

Himejima: Suzaku, the Vermillion Bird (Fire-Bird, or Asian Phoenix)

Kushihashi: Seiryuu, the Azure Dragon

Doumon: Genbu, the Black Tortoise

Shinra: Byakko, the White Tiger

Nakiri: Ouryuu, the Yellow Dragon (Head of the Sacred Beasts, an Earth-Dragon)

The Sacred Beasts are like "Guardian Spirits" for their respective clans. They serve as Familiars to the Heads of the clans, and are passed down from generation to generation. And when the heir to the clan inherits the Sacred Beast, they abandon their given name and take on the name of their respective beasts.