Koyuki is a white Kishu, with a red collar and dark amber eyes.
She's a very kind dog and who cares a lot about her family. She is a gentle dog that convey a lot of loved ones and do not want to upset anyone's view.
Ginga Densetsu Weed
While searching for her younger brother, Kotetsu, Koyuki gets caught in a trap. Weed frees her, and she quickly becomes attracted to him. She returns home and talks to her half-sister Chako, who recently had met the Shiba, Sasuke.
Together, they decide to search for Weed and Sasuke. However, they discover Weed and Kotetsu in a battle with the stray Yuusuke and his gang. Afterwards, she meets with Weed frequently. Gin, however, is worried for Weed as he thinks he is only seeing her because of Koyuki's resemblance to Sakura. Gin informs Koyuki of this and tells her that Weed may not love her as he only sees his mother in her, which upsets Koyuki but she tells Gin she doesn't deserve to be with Weed.
The other Ou dogs don't believe this and want them to be together, yet Weed is also questioning whether he loves Koyuki for who she is or just because he longs for his mother again. Soon, Koyuki's owner sends her away to become a breeding dog. However, Weed follows the car and frees Koyuki, admitting he loves her for who she is and wants to be with her, to which an overlooking Gin agrees to Weed and Koyuki's love.
Together, they take off and enjoy the freedom of life and love. They visit Weed’s mother’s grave and Koyuki buries a fish near it, as her way of paying respect.
Shortly after, their little vacation is interrupted by Rocket who tells them of a growing threat in Hokkaido (the German Shepherd, Viktor). Weed leaves Koyuki in the care of her brother Kotetsu. Koyuki mourns his departure, but understands that Weed has certain duties as Supreme commander of Ohu.
Battle of Hybrid Bears
After the war against the Russian war dogs in battle Koyuki and Kotetsu is seen in the woods that rabbit, and they face a guest red puppy. A short time later appeared on the scene a hybrid bear, and followed by four dogs, whose leaders they initially mistook Weed because of the apparent resemblance. Soon arrived in Weed himself and found out that Weed resembling a dog was thought to be dead Weed's brother, Joe. Joe introduced the guest puppy his son, Koshiro. Soon the dog's owner called them, and they went away from the scene.
Later, when Weed went to meet his brother, Koyuki and Kotetsu were two of the woods. They collided Liger's hunting group, which is designed hated hybrid felling. Liger decided to use Koyuki and Kotetsu feeds, and they were in great danger. Jerome, Lydia and Weed came to help.
Weed's troops decided to help the next river hunting groups to put down the hybrids. Koyuki stayed security to a cave with Koshiro, GB, Sasuke, Lidiya and Kotetsu, but later the majority of hybrids found them. Koyuki tried to attack the bear attacked, but just hit it off. After this, Koyuki and wounded Lydia was taken to the care of people.
Birth of The Puppies
At the end of Hybrid Bear battle, Weed was believed to be dead and Koyuki was about to commit suicide by jumping off a cliff, but Joe stopped her. Lydia reminded Koyuki that by killing herself she would kill her puppies at the same time, and thus it was revealed to all that Koyuki was pregnant. Koyuki was returning Ōu with the other, when Weed and other Ou army came back alive. Koyuki and Weed hugged each other happily.
Ginga Densetsu Weed: Orion
Koyuki survives the volcanic disaster but her mate, Weed, gets wounded as he rescues her. The two stay with her owner in a village who knows Koyuki, as they refer to her by her name. Frequently, they are visited by their children and family.
Over time, Weed is fully recovered from his injury and leaves Koyuki in the care of her owners so he can find his army and lead them in the battle.
Ginga: The Last Wars
Koyuki is at the Akame Mountains with her children, who are training in the sacred grounds. When they begin to wander down a mountain path, they hear a howl from the hills and Akame falls down, injured and exhausted. He warns them that the son of Akakabuto has attacked Ou and the army is in great danger. Orion heads to Ou with his friends whilst Koyuki stays behind with Bella to take care of Akame.
After her sons left for Ōu, Akame wakes up she leaves with her daughter to keep a close eye on him on his way back to Ou but she is told by Akame to stay in Akame Mountains.
- She resembles Weed's mother, Sakura in both looks and personality. This is ultimately one of the reasons why Weed doubts their relationship for a while.
- Koyuki, Kotetsu, and Chako all share the same mother, but Koyuki and Chako have different fathers.