Rumi Satō is a minor character.
Rumi attends the burial of her father Yoshito that he brother Shinjirō arrange. There she meets her niece Anju, and feels sorry she can't do more for her,after she signed the papers that all insurance shall go to her brother. When she gets home, her husband yells at her and beats her for sign off the insurance. Outside the door she sees Anju and Jirōmaru and tells her story. She promised she would come later after her husband falls asleep and leaves her and the pup at a park and calls Seisaburō to inform him what happens and leaves Anju with her cellphone. But her son Yūta had an asthma attack so she didn't return during the night. She arrives in the morning, but Anju's not there. Luckily she's found by the GPS tracker in the phone she left with her.
Nineteen years later, she's at Jirōmaru's Memorial Hospital with her brothers and son, and greets an adult Anju, who's become a doctor.