Hiroko was one of Mari's three pups and the only female in the litter.
Ginga Densetsu Weed[]
Once a human captured Shōta and Mari told the two other puppies to stay at the mountains so she could go feed Shōta. One time the human saw Mari feeding her pup and the human struck Mari in anger. Mari was badly wounded, and tried to find the Ōu army to help her. Luckily some Ōu soldiers that were returning from Hokkaidō met Mari and she asked them for help. Weed brought the hiding puppies to their mother and then saved Shōta and the other dogs with Rocket, Kyōshirō, Sasuke and GB.