He is the son of Kisaragi, the nephew of Hazuki, Minazuki and Uzuki, and the uncle of Harunobu, Hiroshi, Kuranosuke, Masami and Masaru. In the Manga he's the eldest brother of Denshichi, Izō, Kazuki, Miu, Shinsaku, Shūsaku, an unnamed brother, another unnamed brother, and ten other brothers. In the GDW Anime he's the brother of Izō, Kichinosuke, Kogorō, Shinsaku, Shintarō and Shūsaku.
Saburō is a black-and-white Alaskan Malamute/Siberian Husky mix with blue eyes. He looks a lot like his father but with a white muzzle and without the stripes.
He is vengeful towards Masashige, as the white dog caused the deaths of his father and brothers Shinsaku and Kazuki.
Saburo and all the Mutsu brothers are sent to Hokkaido with the Ohu soldiers to help the dogs under Hakurō who were getting invaded by the Russian Army dogs. Nine of his brothers were killed in battle, but Saburo survived.
Saburō remains with his brothers when he hears about the death of his father and swears revenge on the Kurohabaki Clan. Travelling with Izō, he comes across a young puppy in the snow, dying of hypothermia. Izō instantly recognizes the pup as his son and the brothers try to warm him up to keep him alive. Before he dies, the pup reveals his siblings and mother were killed by Masashige under the orders of Kurohabaki Masamune. Saburō follows his brothers and Orion when they encounter Masamune and Masashige, and begin fighting them. Outnumbered, they have no choice but to flee, until they are caught by Masashige at the base of a snow covered mountain. Izō howls to cause an avalanche, which separates the Kurohabaki clan from them, giving them a chance to escape, but at the cost of two of Saburō's brothers who were crushed under the snow. When Masashige is taken prisoner by Tesshin, Saburō wishes to kill him but his request is denied as he is needed alive. Saburō remains close to his brother as he continues to travel and fight the Kurohabaki clan.
After many dogs are killed or badly wounded by the son of Akakabuto, Monsoon, Gin suggests that while the others get away, he acts as a decoy but is told by Jerome and Kurotora not to do it and they will do it instead. Gin doesn't listen and charges at Monsoon, but his Battouga does nothing and Gin is easily thrown off. In a state of panic and anger, the dogs charge at the bears themselves. Monsoon easily slashes at them all, killing Jaguar and badly injuring the rest. Saburō is crushed under the giant bears paws, killing him instantly.
- If going after his name (三郎 transl.: third son), he might be the third-born of the litter.