Ruby was a spirit but now has Wolf body.
Ruby was born a spirit she lived in a ruined city with many other spirits of different sizes but all that came to a end when the city was "cleansed" of spirits by Spirit Hunters, Ruby was not destroyed as she stayed where she was, Ruby never saw her spirit friends again. Ruby was found by Silent during one of her last city checks while Spirit Hunters are to kill any Spirit they see not caring about if they are harmless or not, Silent didn't fire her weapon and left the city with Ruby asleep in her head, which Ruby needed as she hadn't slept since her spirit friends where killed.
Ruby later lived in Johnny roach's head for a while, Johnny called her Ruby because when she blushed her cheeks went as red as the ruby jewel.
Ruby and Johnny now have a boy called Kai.
After her spirit body was damaged Drag had her put into a wolf body, she has a few spirits inside her body but all she says are 100% friendly, she does talk to them from time to time.