Anna was born and raised in Sapporo. Anna's parents died when she was one or two years old so Anna's grandmother took care of her until she too passed away when Anna was two years old. At her grandmother's funeral, Anna sat alone in a corner with her doll that resembled a preteen version of her grandmother crying while her grandmother's acquaintances discussed what to do with Anna, a couple with an infant son was asked to take Anna but they refused and since nobody was able or wanted to care for Anna she was sent to an orphanage with nothing but a blue hairclip her grandmother used to wear and an old photo of her grandmother's childhood home.
Anna was eventually adopted at the age of five by Yoriko Sasaki and her husband. Anna had a happy childhood with her adopted family until she found out that the government sent her foster parents money to take care of Anna, leading the young girl to think that they only took Anna in for money and this lead her to distance herself from her parents. Anna usually called Yoriko "aunt" even though she was her adoptive mother, it is unknown if Anna started doing that before or after finding the money. She also preferred to be alone rather than hanging out with other kids at school. Yoriko believed that Anna's behavior was the result of her being upset because of her adoptive father often being too busy with work.
During a field trip, Anna she is sitting at a bench in a park drawing and after talking with an art teacher who had to turn their attention to another student who had hurt themselves Anna appears to suffer an attack of sorts as she gasps for air and tightly hugs her art book. Afterwards we learn that Anna suffers from asthma. After talking with Anna's foster mother, Doctor Yamashita suggests that Anna takes time away from city life and live in the countryside to help alleviate her symptoms of her asthma even though she school hadn't ended yet so Yoriko sends Anna to a rural town where Yoriko's relatives. whom Anna had only met a couple of times as a young child, live.
Upon arriving to the station, she is greeted by her mother's relatives Setsu and Kiyomasa Ōiwa, who give her a warm welcome and take her to their house in the rural area of their town. Setsu briefly talks to Anna about her own children and allows Anna to sleep in her daughter's old bedroom. After settling down, Anna writes a letter to Yoriko and takes it to the post office where she is spotted by the locals Nobuko Kadoya and her mother but Anna runs away when she notices them.
Anna has short, wavy brown hair and blue eyes. She typically dresses in red shorts, blue sneakers, and a two-shades of blue t-shirt. At the Tanabata festival, she wears a pink yukata that belonged to Setsu Oiwa's daughter.
Anna is a caring, curious, and introspective person. She is an artist, and is often carrying around her sketchbook. The drawings shown in the movie are mostly of landscapes, such as the playground in the beginning, the marsh house, Marnie's house and Marnie herself. Anna has a low self-esteem, deeming herself worthless, ugly, awkward, a nuisance and abnormal. Her social anxiety is also very prevalent, causing her to struggle in large crowds and interaction with people, cutting herself away from others. This is usually mistaken for shyness, but social anxiety and shyness are different things. She suppresses her emotions, usually donning on a neutral expression, and is also very prone to emotional outbursts, suddenly changing moods. Upon befriending Marnie and Sayaka, Anna starts to open up and becomes slightly more upbeat, smiling more and even calling Yoriko her mother.
- Marnie's parents (Unnamed biological great-grandparents)
- Kazuhiko (biological grandfather)
- Marnie (biological grandmother)
- Emily (biological mother)
- Emily's husband (biological father)
- Yoriko Sasaki (adoptive mother)
- Mr. Sasaki (adoptive father)
- Setsu Oiwa (possibly aunt or cousin once removed)
- Kiyomasa Ōiwa (possibly uncle or cousin-in-law once removed)
- Oiwa children (adoptive cousins)
- Both Anna's birth and adoptive fathers remain nameless through the movie and were only seen in either pictures or flashbacks.