He has greenish-brown eyes and pale red fur.
Like his uncle Weed, he is calm and polite and very excited to know that he has other family members.
Ginga Densetsu Weed
He was born in the mountains along with his three brothers, but his brothers and Hitomi were killed the Hybrid Grizzly Bear.
Joe realized that one of the puppies survived and named him "the happy fourth son", so he could live happy, not just for himself, but for his brothers.
Kōshirō became Ninomiya's pet, just like his father, and was called "Chibi" by him.
Later, Kōshirō was taken to safety during the battle against the hybrid bears. After the battle was over, Kōshirō went to live in Ōu with his father.
Ginga Densetsu Weed: Orion
When the volcanic eruption destroys Ou, Kōshirō is seen fleeing with the other Ou warriors.
After that, he is not seen or mentioned in this series, as such it is unknown if he survived the volcano eruption or not.