Yoriko and her husband adopted Anna when she was five years old. Yoriko was euphoric over finally becoming a mother but was worried about not being able to care for her new daughter right so she constantly called her relative Setsu Oiwa all the time to ask for parenting advice. The family of three lived a happy like until Anna turned twelve and she distanced herself from her peers.
Yoriko is present when Anna is being examined by the doctor in her bedroom after Anna suffers an asthma attack during a field trip. When Anna is put on bed rest, Yoriko offers the doctor tea and talks to him about how Anna has become distant of her and her father over the last few years and worries that it's because Mr. Sasaki is often busy with work or because they and Anna are not biologically related. The doctor then suggests that Anna should spend the summer in the countryside to help her asthma condition so Yoriko does just that and sends her adoptive daughter with her relatives who leave in a small, coastal town right school ends, she gives Anna lots of snacks to eat during the trip and some letters so that they can write to each other.
When Anna meets a girl named Marnie, Anna reveals that she found out that the government sends her adoptive parents money to care for Anna, leading the young girl to think that they only took her in for money. Right after that Yoriko comes home and gives Anna a box of color pencils and Anna smiles half-heartedly.
Yoriko is a loving mother who does her best to make sure Anna is healthy and happy, even sending her to the seaside for three months to help Anna with her asthma. She is also very emotional, often disorving to tears under stressdul situations.
- Unnamed husband
- Anna Sasaki (foster daughter)
- Setsu Oiwa (possibly sister or cousin)
- Kiyomasa Ōiwa (possibly brother-in-law or cousin-in-law)
- Setsu Oiwa's children