As a puppy like his youngest brother Weed, Yukimura was kind-hearted too but he felt great responsibility as the eldest sibling and was very mature for his age.
Yukimura appeared to suffer from PTSD after the attack from the monkeys at a young age. Growing up, he was very stubborn and acted like a genocidal maniac because of his PTSD, even refusing to listen to his adoptive father, Saheiji. Whenever they had a talk about the monkeys, he seemed to have cared a lot about Weed and Joe after finding out Weed was his brother from Saheiji. Much like Riki, he is also strict.
Even though, he knew Gin was his real father Yukimura greatly honored Saheiji as his father.
When it comes to strength of numbers he has a sense of honor believing that the bigger army won't always win. Also when fighting he can be slightly overconfident.
Right before his demise Yukimura sees that not all monkeys are bad when the rebellious tribe attack Shogun which could mean he is a bit humble when admitting his mistakes.
Ginga Densetsu Weed
Even at a very young age, Yukimura felt great responsibility as the eldest son. He could eat solid food at an unusually young age and learned to catch small nonvenomous snakes.
However, his mother soon became ill and had to ask a wandering dog named Saheiji to take care of her puppies. Saheiji then adopted the oldest of her puppies: Joe and Yukimura.
Yukimura knew Gin was his biological father, but he saw Saheiji as his real father. After departing from his mother and youngest brother, he swore to take care of his other brother and keep Gin's bloodline alive.
Yukimura, Joe, and Saheiji moved to Saheiji's territory in Nagano Prefecture. One day, the three were attacked by Shōgun's macaque minions.
Saheiji ordered his sons to run, but Joe was captured and the macaques started to beat him with sticks. Yukimura tried to help his brother, but he too was hit and his head was scarred.
Saheiji protected young Yukimura, which resulted in disabling his lower body. Barely conscious, Yukimura saw how the macaques dragged his brother away and believed that he died. Yukimura was very shocked by the fact that he couldn't protect his younger brother. His personality changed greatly and he swore to kill all the monkeys.
As a leader
After Yukimura grew older and stronger, he became the next leader of Saheiji's pack of sixty dogs. Although he was the leader, he greatly honored his foster father and saw him as the highest member of the pack. Hōgen once wanted to ally with Yukimura, but he refused. Yukimura hated dogs who threatened others with large armies, for he believed it wasn't the number that made a true army.
Although Yukimura still had some honorable traits left, his judgement was clouded by his hatred and thirst of revenge. Due to his past experiences, he hated all the monkeys and believed that they were all bad. He called them "dog eaters", even though his own pack killed and ate monkeys, including babies.
This seemed to be more like a fun sport for Yukimura's pack, because they already had several other prey animals. Yukimura even created a technique, Neck The Killing, to kill monkeys more effectively. He also came up with a cruel training method, one each of his pack members had to pass, which included torturing and killing monkeys.
Yukimura's minions were extremely loyal to him, as they too had lost close ones to the monkeys and shared his goal to kill all of them. Saheiji didn't agree with the goal, but Yukimura refused to listen to him.
Meeting with Weed and the Ōu army
Around the age of one year, Yukimura meets the Ōu warriors. Yukimura and his pack rescues Jerome, Kōji, Kōichi, Kazuo and then Weed, Sasuke, Kyōshirō and GB from the monkeys. Yukimura is shocked by how much Weed resembles Joe and realizes he must be his long-lost brother. Still, he doesn't reveal this to the others and leads them to his pack's home, which is an abandoned mine.
Yukimura offers Weed and his friends some food and introduces them to Saheiji, but he is distrustful of the guests as he thinks they're on the side of the monkeys. Yukimura wishes to train the three puppies and asks Weed and his friends to wait outside the training area. Jerome, who was accepted into the pack, follows Yukimura and is shocked by the cruel treatment of Pepe, a young baby monkey.
Jerome tries to stop the training, but is easily defeated by Yukimura.
Weed and his friends arrive to the scene and Yukimura reveals to them that the food they ate included meat of Pepe's parents.
An old macaque called Gozaru appears and tries to tell the dogs that Shōgun is behind everything. Still, Yukimura doesn't change his mind about the monkeys, and gets into a duel with Weed.
Yukimura wins the fight and informs Gozaru and Weed's friends that he'll march to war against Shōgun in three days. It's later revealed that Yukimura is wounded from the fight, though he hid it earlier, and needs three days of rest.
The next day, Yukimura saves Sasuke from the monkeys, but refuses to help Weed and Jerome to rescue Pepe, who is kidnapped by Tobizaru. However, Saheiji makes Yukimura change his mind.
He also almost reveals who is Yukimura's real father, but the young dog refuses to hear it and tells Saheiji that he's the best father anyone could ever have. After that, Yukimura attacks Shōgun's base with his army, in order to avenge his foster father, not to help Weed.
During the battle, Yukimura sees the macaques fighting against Shōgun, and he finally changes his mind about them. He uses Neck the Killing on Shōgun's neck and, in his over confidence he believes it was enough to kill the giant baboon. However, Shōgun isn't badly wounded and manages to surprise Yukimura while he is checking on GB's condition. Yukimura is stabbed through the stomach with a branch, but is saved from death when Weed attacks Shōgun.
Jerome drags Yukimura to safety and tells him not to move, but Yukimura doesn't want to give up and pulls the branch out. Upon his request, Jerome takes Yukimura to the top of the cliff, where he tells Jerome to go back and tell Weed to use Battōga as a sign. When the time is right, Yukimura leaps off the cliff and uses his Battōga to scalp Shōgun.
The dying baboon is killed by the remaining macaques as Yukimura lies on the ground, dying from his wound. Saheiji, who met Gin and is carried to the battleground, tells everyone that Yukimura is indeed Gin's son and Weed's brother. Gin respects Saheiji as Yukimura's true father and lets him speak to Yukimura.
Weed begs for his brother not to die, but Yukimura is unable to hear nor answer. He remembers the harsh, but happy childhood he spent with his mother and his brothers. The rain stops as Yukimura passes away and the dogs howl for his memory.
Weed attempts to take Yukimura back to Ōu to bury him where their parents used to live, but Gin talks him out of it saying that Yukimura was raised in this land by Saheiji. Weed then agrees and informs everyone that Yukimura will be buried in the mountains. The next morning, the monkeys help bury his body and Pepe apologizes to Weed for what happened.
See more pictures in Yukimura/Gallery.