Kinumaru was the daughter of one of Gin's siblings, most likely the white dog. She is mother of Zion and 8 unnamed pups.
She is called Shiro by Kenta.
She is a white Akita Inu like one of Gin's Siblings, Yuki, and her son Zion.
Winds of Zion
She used to be a pet dog, however, she was abandoned by her humans after about a year. She became a stray that lived in the city on the streets. Here, she met the male, Billy, whom she fell in love with.
He taught her how to survive on the streets, bringing her food and showing her where the best water sources were.
Soon, she gave birth to nine healthy puppies and together with Billy, she raised them. However, Billy one day disappeared and that was the end of the happy family.
Eight out of the nine puppies died, leaving her with only one pup, Zion, and Kinumaru herself slowly started to wither away from hunger and illness.
She died shortly after. Until the end, she believed that Billy would return to provide for his family.
Ginga: The Last Wars
Zion mentioned that when she was alive, she told Zion about her heritage in the bear hound family.