Saheiji is a grayish brown dog with black eyes. His ears are ripped.
Saheiji helped a new mother dog named Sakura to get some food for her and her three pups. When he was about to leave, Sakura asked him to take her pups. Though one pup continued to suckle from her, so Saheiji took the other two and adopted them, naming them Joe and Yukimura. He moved to his home area with the puppies but there they got attacked by Shōgun's macaques. Saheiji protected Yukimura with his own body as the macaques started to hit them with sticks and rocks. Saheiji's pack showed up and drove the macaques away, but Joe had already been taken away and Saheiji's entire lower body was paralyzed because of the hits. Yukimura's personality changed and he started to hate all the monkeys after what happened, wishing to kill them all. Saheiji didn't agree with this goal and was saddened by the change in Yukimura, but Yukimura refused to listen to him. Yukimura eventually inherited the leadership, though he still honored his adoptive father as the highest member of the pack and its true leader.
Many months later, Saheiji meets Weed when Yukimura brings him to a abandoned mine that is their home. When Yukimura's pack tortures a baby macaques named Pepe and treats their guests badly, Saheiji tries to talk sense to them, which seemingly works. However, in truth, Yukimura plans to use Weed's pack in his own war against the monkeys. Saheiji talks with Yukimura again and attempts to reveal the identity of his real father, but Yukimura doesn't want to hear it and tells Saheiji that he's the best father anyone could have. Saheiji tells Yukimura to go and help Weed in the fight against Shōgun, and Yukimura does. Shortly after, Saheiji meets Gin and his pack and tells them of Sakura, Yukimura and Weed. He is carried by Hiro to the battle ground where he sees Yukimura, his beloved adoptive son, die. Saheiji reveals to everyone that Yukimura and Weed were brothers. After Yukimura’s death, mournful Saheiji seems to lose his zest for life and he only wishes to be buried next to Yukimura after he dies. Later, Joe visited Echigo and Saheiji told him about Yukimura's death.
After Noah predicts a meteor will impact the Japanese mountains where the dogs live, he foretells that Weed knows a place where they can seek protection. Weed says it is Saheiji's mine, as it is big enough to house the Ou Army. Once arriving, Saheiji welcomes them in and invites them to stay at the mine. As the meteor strikes, earthquakes rattle the entire mine, shortly followed by forest fires. As the destruction goes on, Saheiji retells the story of Yukimura to Orion and Rigel, saying he was a heroic dog and made peace with the dogs and monkeys. As the earthquakes come to a stop, it begins to rain black raindrops.