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. When Anna's new parents brought her home, Yoriko was euphoric and wanted to make up for the five years she didn't spend with Anna so she taught Anna lots of things like using a knife, although she always got worried about something and often called Setsu for help. Overall, Anna a happy childhood with her adopted family.
One day Anna found out that the government sent her foster parents money to take care of Anna, leading the young girl to think that the couple only took Anna in for money and this lead her to distance herself from her parents as well as calling Yoriko "aunt" even though she was her adoptive mother. 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 or them not being blood related to her.
During a field trip, Anna is sitting at a bench in a park drawing and after her 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 called Kissakibetsu to stay with Yoriko's relatives, whom Anna had only met a couple of times as a young child.
Off to Kissakibetsu
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 quietest part of 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. As she runs, Anna sees an abandoned mansion across a salt marsh and goes to investigate. She looks around, finding it familiar, but gets trapped there by the rising tide until she is found by Toichi, a taciturn old fisherman. Setsu tells her that the mansion used to be a vacation home for wealthy foreigners, but it has been empty for a long time and the townsfolk believe it to be haunted. Starting that night, Anna dreams of seeing a blonde haired girl in the mansion.
On the night of the Tanabata festival, Anna gets mad at Nobuko Kadoya when she reads out loud Anna's card where she wrote that she wished to "live a normal life" and when she got too close to Anna to see her blue eyes Anna grew overwhelmed and called her a "fat pig" and ran away to the mansion where she meets the blonde haired girl named Marnie. The two agree to keep their meeting secret and they meet again on the next evening. Anna returns to the Oiwa residence to find her aunt being yelled at by Nobuko's mother, who complains about Anna insulting Nobuko and lying about Anna threatening her daughter with a knife, although her uncle and aunt don't believe her and don't punish Anna but instead urge her to apologize to Nobuko for insulting her. The next night, Marnie invites Anna to a party at the mansion. While there, Anna sees Marnie dancing with a boy named Kazuhiko. Later, some townspeople find Anna asleep by the post office. Anna returns to the mansion but it appears abandoned and dilapidated again.
A week later, Anna meets Hisako, an older woman who paints pictures of the marsh and the mansion. Hisako comments that Anna's sketches look like a girl whom she knew when she was young. She also tells Anna that the mansion is being renovated for new owners. Anna runs to the mansion where she meets a girl named Sayaka, who discovered Marnie's diary hidden in a drawer.
The next day, Marnie reappears and the two girls discuss their home lives. Anna admits to finding government documents that show how her foster parents are paid to take care of her. Anna makes the assumption that they only pretend to love her for the money. Marnie then shares with Anna how her mother and father are always traveling abroad, and how she is always left in the mansion with her nanny and two maids. The maids abuse her, and threaten to lock her in the silo near the mansion. Anna leads Marnie to the silo, where she helps her confront her fear. Anna wakes up, only to find Marnie gone.
Meanwhile, Sayaka finds the missing pages from Marnie's diary, which include passages about Kazuhiko and the nearby silo. Sayaka and her brother find Anna unconscious and bring her back to the Oiwas. In her feverish state, Anna dreams about confronting Marnie, who tells Anna she is sorry for leaving her and that she cannot see Anna anymore.
When Anna recovers from her fever, Sayaka shows her the missing pages and a painting Hisako gave to Marnie. They converse with Hisako, who tells them about Marnie's story: Marnie married Kazuhiko and they had a daughter named Emily. Kazuhiko died from a sudden illness and Marnie committed herself to a sanatorium. With no other family to care for her, Emily was sent to a boarding school at a young age. Marnie recovered but Emily blamed her mother for abandoning her. Emily ran away and had a daughter herself, but she and her husband were killed in a car accident. Marnie raised her granddaughter, who was placed in foster care after her death.
At the end of the summer Yoriko arrives in town to take Anna home. She gives Anna a photograph of the mansion and says it belonged to Anna's grandmother. When Anna sees Marnie's name written on the back, she realizes that she is Emily's daughter, and thus Marnie's granddaughter. This revelation helps to bring Anna closure about her identity. Yoriko also tells Anna about the government payments, but reassures her that they have always loved her regardless. For the first time Anna calls Yoriko her mother.
During the end credits, Anna says goodbye to the friends she met in town and apologizes to Nobuko for her harsh words before seeing Marnie at the mansion window waving goodbye to her.
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 although at first she believed that she wasn't good at drawing when in fact she is great at it. 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, which is is usually mistaken for shyness. 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, apologizing to Nobuko for hurting her feelings 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 (possible aunt or cousin once removed)
- Kiyomasa Ōiwa (possible uncle-in-law or cousin-in-law once removed)
- Oiwa children (adoptive cousins)
- Both of Anna's birth and adoptive fathers remain nameless and were only seen in either pictures or flashbacks.