Mimi is a thirteen-year-old middle school student of Japanese and African American descent. Moving from a diverse city in California to a predominantly White town in Vermont, she struggles to find a sense of belonging in a community focused heavily on her race. She is passionate about science and dreams of becoming an astronaut. She respectfully pushes against the gender and racial expectations of her new environment, particularly by expressing interest in the boys-only wood shop class.

James is an African American college professor who moves his family to Vermont for a new teaching position. He provides steady, calm guidance to his daughter, teaching her that peaceful, consistent effort is more effective than forceful demands. He frequently cooks and bakes at home, quietly subverting the traditional gender roles of the era.

Emiko is Mimi's Japanese mother who grew up in Tokyo before marrying James. She is deeply connected to her cultural traditions, cooking Japanese meals and observing customs like the hatsuyume. She is initially hesitant to interact with her new neighbors in Vermont, fearing discrimination and preferring the safety of her home.

Stacey is a middle school student who recently moved from Georgia to Hillsborough because her father accepted a college teaching position. She quickly becomes Mimi's best friend, bonding over their shared status as newcomers. She speaks with a southern accent and demonstrates loyalty to Mimi, though she must carefully handle her traditional mother's strict rules.

Timothy is a boy from New York who spends his school vacations staying with his great-uncle in Vermont. He treats Mimi normally, showing no prejudice or excessive curiosity about her background. He harbors a secret interest in learning how to cook and bake, a hobby he pursues quietly to avoid judgment.

Mr. Dell is the Olivers' gruff and solitary neighbor. He initially avoids interacting with the family and speaks harshly to Mimi when she approaches his property. He lives alone with his dog and frequently works with tools in his garage.

Mrs. Stanton is a supportive science teacher who organizes the school's annual Science Groove. Unlike others who dismiss Mimi's ambitions, she actively encourages her dream of becoming an astronaut. She relates to Mimi's passion, having abandoned her own scientific dreams due to societal pressures against women.

Auntie Sachi is Emiko's relative from Berkeley, California. She represents the vibrant, supportive community Mimi leaves behind. She carries painful memories of being placed in relocation camps during World War II, a history she shares honestly in spite of others' attempts to suppress it.

Uncle Kiyoshi is Auntie Sachi's husband. He is a pragmatic man who manages the family's property in California and prefers to focus on the present rather than dwelling on the painful history of Japanese American internment.

Shelley is one of Mimi's Japanese cousins. Growing up in California, the two shared a backyard and practically lived in one house. She provides Mimi with a strong sense of cultural identity and childhood joy.

Sharon is Mimi's other Japanese cousin in Berkeley. She, along with her sister, taught Mimi Japanese phrases and shared games that keep Mimi connected to her heritage even after moving across the country.

Dr. Haseda is a Japanese professor at Hillsborough College. She is outgoing and helps draw Emiko out of her isolation by encouraging her to teach a class on the Japanese tea ceremony. She has a young daughter named Kate.

Kate, affectionately nicknamed Baby Cake by Emiko Oliver, is Dr. Haseda's one-year-old daughter. She provides Mimi with an opportunity to take on babysitting responsibilities.

Victor is an intelligent, quiet student who stands out as the only African American male in the middle school. He keeps to himself and reads books like The Autobiography of Malcolm X, remaining composed even when targeted by bullies.

Mrs. Lavoie is Stacey's mother, who holds traditional, old-fashioned views about race and social etiquette. Her prejudices initially prevent her from allowing Stacey to invite Mimi over, causing friction in the girls' friendship before she eventually meets Emiko Oliver.

David is a student in Mimi's grade who harbors prejudice against Japanese people and fiercely competes in the Science Groove. He frequently instigates conflict and bullies others who step outside of the community's rigid social norms.

Mr. Sperangio is the strict wood shop teacher who refuses to let Mimi use the classroom tools. He firmly believes in the school's gender divisions and threatens disciplinary action when Mimi and Stacey attempt to sit in on his class.

Mr. MacDougall is the school principal who enforces the disciplinary consequences of Mimi and Stacey's peaceful protest. He initially dismisses their complaints about gender-segregated classes as silly rebellion before realizing the depth of their commitment.

Wesley is Timothy's older brother who considers joining the military. His military service hangs over Timothy's time in Vermont, serving as a source of quiet anxiety for his younger sibling.

Pattress is Mr. Dell's dog. Despite her owner's gruff nature, Pattress eagerly befriends Mimi and Timothy, acting as a bridge between the isolated older man and the children next door.