Eiko lives in the village in Akita with her family. She takes care of Yamabuki with her husband.
When Gohē Takeda comes to take away one of Yamabuki's puppies (for training), she is worried and asks her husband to do something. She is glad to keep little Riki when all the other puppies get new homes and he isn't wanted.
When Yūjirō's big sister asks to have Yamabuki back, the whole family drives to see her and give her both Yamabuki and Riki. Tōru wishes they could keep Riki but Eiko scolds at him by mentioning that he never participated in taking care of the puppy and just played with him. She also mentions that she will miss Yamabuki and Riki too.
While Yamabuki is given back, the Bizen family decides to keep Riki after all. Riki tries to run back to see his mother and gets wounded in the fight. Eiko is shocked to see the little puppy with wounds and quickly calls his husband to come and see.
Eiko isn't seen nor mentioned in the story after this, but it's known that her family kept Riki for about 3 years before he was given to Gohē to train.