He is a former pet dog and a current member of the Ōu Army. Although he is an Iga Ninja descendant of the 114th generation, he was never teached the Iga Ninja Techniques. But he still has those attributes in his blood using his own Ninja Techniques.
He closely resembles the great leader of the Iga ninja dogs, Akame, except that he has two small circles on his forehead.
With hearing great stories of their grandfather Akame and their ancestors. Shirozaru like his brothers greatly admires and deeply respects Akame. He is also quite understanding when their mother forbid them from looking for Akame in hopes of keeping the next generation of the Iga clan alive.
Ginga Densetsu Weed: Orion
During the war with the Kougas, Akame decided to adopt all Iga puppies younger than six months of age as his own, which included Shirozaru's mother. He made them swear to never return as an Iga ninja dog. Shirozaru's mother obeyed her father, but proudly taught her children the great stories of their ancestry, and about the great leader Akame.
Numerous times, Shirozaru wanted to join his grandfather, but was stopped by his mother, until he heard about the volcanic eruption in Ouu. Since Akame is believed to be dead, he is finally allowed to go.
Along with his brothers, Mū and Rara, they head toward the Ouu mountains to find any survivors, including their grandfather. When they have arrived, they encounter Sasuke, who was in trouble with Kamakiri's sons. When Akakamakiri tried to attack Shirozaru, he grabbed Sasuke, and, along with his brothers, did a ninja jump, kicking snow in the evil army's faces. He asked Sasuke to lead them to the shed to help protect Weed's pups and told him about Akame's desire to continue the generations of the Iga ninja dog clan, in which he was told years ago.
But when they got there, the pups were nowhere in sight. Shirozaru and his brothers offer to help Sasuke round up the pups, and they set out to find them. The first pup they encounter with is Bellatrix, who is being kidnapped by a Kurohabaki clan member. Izou and his brothers are also there to help. When the evil dog leaps over Shirozaru, he jumps up after the dog, and grabs Bella.
Later, Shirozaru and his brothers make contact with Izou and his brothers. While Izou's brothers and Shirozaru's brothers look after Bella, he, Izou and Sasuke continue their search to find any Ohu survivors. On their way, they bump into Ryo's cronies, who were torturing Heizō, one of Orion's comrades.
To save the unlucky golden husky, they attack the rogue dogs and easily defeat them, managing Heizo to escape. Ryo and his comrades decide to tell them about their relations with the Kurohabaki Clan and they now know a new threat is about to emerge.
As they continue their search, they encounter several Kurohabaki clan members, discovering that they are violent and strong fighters. They also spy a bit on their hide out, also discovering about their leader, Kurohabaki Masamune and his incredible strength. The three Ohu soldiers decide to head back the shed and they eventually encounter Orion and his friends. Because of Orion's hasty behavior, Izou stops him and they all head back to the shed.
When Orion woke up, they all introduce themselves and Shirozaru explains the situation. Since they are the only hope to find Orion's pack and to reestablish the Ohu paradise, Shirozaru decides that they should find as many fighters as possible to join them to both defeat the Kurohabaki clan and to find the Ohu survivors. During the Kurohabaki clan arc, he participates in both wars against Masashige and Kamakiri's sons.
Ginga: The Last Wars
Shirozaru accompanies his brothers to Ou when they hear about Monsoon attacking the Ou Army. The three dogs find Cross under the care of Daisuke and hear about the situation in full. When Cross notices Bob spying on them, she sends the brothers to chase after him and they succeed in catching up to him to question his motives. Bob escapes them once again and they chase him to the prison where the Ou dogs are being kept. The brothers help fend off the bears with Ogasawara Gennai and Zion.
Sometime later, a flood causes a wounded Ken to be washed into a river and the Ou army go to the location to find and save him. They each keep a watchful eye on the raging river, as Kawasemi dives in to find him.
He sees that the bears get scared off by the arrival of humans and Unsai get carried away for treatment his brother Rara and others begin to ask him what should they do and did they lose. Shirozaru informed them that their grandfather wasn't dead yet and tells his brother not to jump to conclusions.
Shirozaru and his brothers follow Kawasemi as he leads the charge to finish off the rest of Monsoon's Kin. After all of Monsoon's Kin is defeated, Akame collapses onto the ground and Shirozaru and his brothers rush to their grandfather's side hoping he was alright, they watch their grandfather drift in and out of consciousness until he is revived by Daisuke and Hidetoshi realizing their grandfather needs help. He watches silently as his grandfather is taken away for treatment with Izou.
Sometime later, Shirozaru watches with his brothers and their comrades as the humans bury their fallen comrades along with paying their respects.
He and his brothers are reunited with Lord Gin and the rest of the soldiers; then the akita informs the group of some of their friends passing and is seen sleeping with everyone in the night until Gin wakes up from a nightmare and notices that their friends haven't returned.
When morning comes Shirozaru hears Kyoshiro chew Orion out for sending his friends away. Then, watches Kyoshiro challenge Orion to a fight even though the kishu lost he was amazed by the pup's strength. He saw Orion crying in tears saying that he stayed behind for the sake of everyone because the Ohu Army needs a true leader.
Some time later, Shirozaru sees Orion go crazy and purposely fall into valley running after him. But he hears that Jerome is going to bring him back and sees the shepard fall after him. Then, they find Jerome and Orion safe and sound.
After Orion's returning visit from Akame and the others, he hears that everyone is doing well. Shirozaru 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, Shirozaru 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.
Shirozaru 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.
Then, sometime later taking a break in their training Shirozaru and the others find Chibi sleeping by Rigel. After that he hears from Cross that a hawk-eagle has come looking for prey and shows concern wondering where Orion is.
Shirozaru and the others locate Orion and to find that he has slained the bird. He goes to his grandfather to inform him of Orion's progress and Akame tells him to tell Orion to keep practicing.