Anna has short brown hair and blue eyes. She typically dresses in tan 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 and the marsh house, and of Marnie. 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.
When we first see Anna she is sitting at a bench in a park drawing, after conversing 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 conversing with Anna's foster mother Yoriko Sasaki, Doctor Yamashita suggests that Anna take time away from city life and live in the country to help alleviate her symptoms of her asthma.