Shirō was a member of Tenka's pack who formed a close friendship with Gennai.
Ginga Densetsu Weed: Orion
Upon Gennai's defect, he left with his friend and two others to help in the fight against Masamune Kurohabaki. Gennai in turn sends Shirō to spy on the Kurohabaki Clan, but he was taken prisoner and taken to Masamune to be tortured by his subjects. Matheus tortures him and tries to get him to reveal the location of Tenka. He rips off Shirō's left front paw, bites off his ears, gouges out his right eye, and cuts off his tail. Even so, Shirō does not reveal anything.
Gennai is worried when Shirō does not return, and leaves with a small army to look for him. On the way he meets the Koga ninja dogs, Tsukikage and Toshimitsu, and thinks they attacked Shirō. However, the Ninja Dogs tell Gennai what really happened and agree to deceive Masamune's pack in order for Gennai to go help Shirō.
Gennai gets there the last minute to rescue Shirō and they return Tenka, but Tenka is unhappy with the failure and tries to send Gennai and the wounded others out again. However, Gennai does not agree and leaves Shirō at the hot springs.