He is the son of Kisaragi, the nephew of Hazuki, Minazuki and Uzuki, have unnamed mate, and the uncle of Harunobu, Hiroshi, Kuranosuke, Masami and Masaru. In the Manga he's the brother of Denshichi, Izō, Kazuki, Miu, Saburō, Shinsaku, an unnamed brother, another unnamed brother, and ten other brothers. In the GDW Anime he's the brother of Izō, Kichinosuke, Kogorō, Shinsaku and Shintarō.
Shūsaku is a Siberian Husky and Alaskan Malamute mix. His fur is reddish-brown with a white belly. His eye color is orange/brown.
In the Anime, his fur is gray with a white belly and his eyes are blue.
Shūsaku lives with his brothers and father in Mutsu.
He is first seen hunting a bear with his brothers and gets bitten by the bear, but survives. After hearing from Shigure about the invasion of Ōu by Hōgen and Genba, he and five (six in the manga) of his brothers are sent to Ōu to aid them.
He and his brothers later fight Genba's platoon and in commando to slay Hōgen.
Shūsaku and all the Mutsu brothers are sent to Hokkaidō with the Ōu soldiers to help Hakurō and his pack who were getting invaded by the Russian Army dogs. Some of his brothers were killed in battle.
Shūsaku 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 Masamune Kurohabaki. Shūsaku 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 Shūsaku's brothers who were crushed under the snow.
The Ōu Army
Shūsaku remains close to his brother as he continues to travel and fight the Kurohabaki clan.
Shūsaku is in Ou some time after the death of Masamune, but peace is disrupted when Monsoon attacks and badly injures the dogs, killing some in the process. Shūsaku survives but is injured and thrown into a makeshift prison with his brother and the Ou dogs.
Many days later, Shūsaku and the rest of the dogs are rescued by Mole and his group. Barely able to walk due to injuries and being cramped in the prison for so long.
Shortly after, Shūsaku and other Ou army are resting in the grass during a storm.
He watches Kage tell his father to leave it to him and will act as decoy. Kagetora tells everyone to get out while he get eaten and will not die at once. Kurotora tells him that's stupid and he's not getting eaten. Kurotora says that he's prepared to die but he's speaking with spirit.
He watches Kagetora charge at Monsoon and bit Monsoon's left eye. Monsoon hit Kagetora, he fell on ground and Monsoon run away. Mel and Akakamakiri ask Kage if he's alright and he says yes relieved to hear that his friend is alright.
Then, he was met by Orion's group and was told that Monsoon was scared off by humans. Shortly after he and the others heard a helicopter from up above, upon seeing it Shūsaku wishes for the humans to give Orion and the others support.
Then, Shūsaku begins to hears the victory howls of their comrades proud of their success they begin to join in too.
Next, Shusaku is seen sleeping in the grass unaware how much time has passed and he goes to see if everyone is alright to which they are. Then, he is alerted by Kurotora that someone is coming thinking it was Monsoon and Akakama stands up to defend them. It turns out it was Orion and Tesshin who tells them that they found Monsoon again but he got away. Once Akakama hears that he points out that they scared him leaving Miu shocked that the dog was afraid. He hears Orion says he'll never forgive Monsoon for what he did and won't let him get away.
Shusaku and the others see hunters searching for any remaining bears and Kurotora tells them not to be afraid and that these humans are they can trust. The Kai Ken tells them not to bite the humans especially Akakama he warns him that if makes enemies they can't work together.
Then, he is treated by Daisuke for his injures along with his father and the others Hidetoshi couldn't take in. With his wounds healed, he and the other injured dogs regroup and are joined by Gin, who left Daisuke's care to check on them. Feeling defeated over their losses, the army spend their days and nights cuddled together for comfort before Andy, Yamabiko, Bon and Orion leave to find Sirius.
Is woken up by Gin having a nightmare discovers that Orion and the others are gone. When morning comes Shusaku 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.
After Orion's returning visit from Akame and the others, he hears that everyone is doing well. Shusaku goes with everyone to search for the lost sickle but after days of searching it's nowhere to be found. With Kyoshiro thinking that Orion isn't leader material anymore they all choose Cross to be the new boss with Kuro agreeing and when Orion returns. He hears Orion say that he is going to learn some new secret ninja techniques he picked up from Akame. Believing in the young pup he follows the others to watch Orion.
Seeing Orion's skills, Shusaku and the others want to try it too, but when they try to take a swing, they don't manage to do the same as Orion. He hears from Orion what he learned in a day took Akame two years to learn. As the training continues, he becomes impressed with Orion's progressed and gets encouraged to keep training. Then, he hears that Rigel and Rocket have returned, but with them are a bear cub. Everyone charges at it, after Kyoshirou attacks it. When he attacks the bear cub, he becomes surprised that Rigel flipped Kyoshirou over with ease. After Rigel explains everything, they all become surprised that Sirius wants them to raise Chibi until he becomes an adult.
Shusaku watches Rigel and Rocket convince Orion not to kill Chibi. Then, hears Orion talk disrespectfully towards his comrades. When he hears that Orion is trying to protect everyone in Ohu. He also sees Orion pointing his bamboo stick at Kurotora convincing the pup to attack him but is stopped by Jerome and watches in horror as Orion almost attacks the shepard. He watches Kyoshiro give Orion a beat crying in tears but soon the tears turn into laughter as everyone runs back up the hill.
- He has been known as Shirozaku, but this is simply a mistake name. The character is Shūsaku both in Ginga Densetsu Weed anime and manga.
- He and his brothers are called Alaskan Malamutes several times in Ginga Densetsu Weed, despite the fact that their father was mentioned to be Siberian Husky. It has since been confirmed he is a mix breed.