Avatars

The Zodiacs are not able to enter the realm of mortals that is to say they cannot without great damage to the world, and so when the gods need to do their act in the world, they each select an Avatar, A mortal who exemplifies the nature of the Zodiac, Their personality, their world view, these are usually followers of the god. It it an honour among many to be chosen to be the vessel for a god. how we view the zodiacs today is based upon the mortal forms they have taken in the past, explaining why so many of them look humanoid.
The most notable time that this happened was when Ophiuchus betrayed the zodiacs, having been cast down by the other zodiacs Ophiuchus fled to the mortal realm under the guise of Shale Enro and hid himself from the others.
When the Zodiacs discovered this, they chased him, each of the thirteen adopting a Avatar, a Champion of themselves to hunt down Ophiuchus.