Though it was once a dragon, by its own will it decided to become the steed for a virtuous priest.
It was once the child of the Dragon King of the Western Sea.
As it has inherited the Dragon King's blood, it is able to control all sorts of water, and possesses a power that surpasses that of human understanding.
The white horse stayed close all through the priest's journey.
In the past, and even now, in a faraway time and space.
Like the devas, it is always with the respected priest--- even if it should lose its form!