Koroku is one of the ten Sanada ninja dogs. He apparently guards their territory on the border, as he always informs others if there are intruders or strangers.
Personality
Ginga Densetsu Weed: Orion
Ginga: The Last Wars
Koroku is seen with Sanada Nyūdōunsai on a nightly patrol when they encounter Reika and her children. Reika explains that Ohu has fallen because of the bears attacking them, who are the children of Akakabuto.
After Lord Unsai is taken away for treatment, Monsoon's Kin are dead and with Gin's return he tells them the passing of their friends they all sleep together for the night.
When morning comes Koroku hears Kyoshiro chew Orion out for sending his friends away and then watches the fight by Orion and Kyoshiro even though the kishu lost. He saw Orion crying in tears saying that he stayed behind for the sake of everyone because the Ohu Army needs a true leader.