Koshiro is one of Joe's four pups, the only one alive.

Koshiro and his siblings, together with their mother, were attacked by a hybrid bear while their father Joe wasnt around. Mother and siblings died but Koshiro survived. He became a pet and hunting dog just like his father. He met Koyuki and her brother while hunting and, later on, his uncle Weed too but Joe didn't want to be in any term with him and beaten up Koshiro when he wanted to see uncle Weed once again. He didn't join the battles with the hybrid bears but, when they were over, Joe took him to Ohu to live there.

He did not appear in the sequel GDW:O but he is supposed to be alive.