Amanda is an eleven-year-old girl who feels increasingly alienated after a falling-out with her former best friend, Leo. She harbors anxieties about her social standing, which drives her to endure stressful gymnastics tryouts instead of pursuing her true passion for the marching band. When she wakes up to find her disappointing eleventh birthday repeating itself, she begins looking for a way out of the bizarre time loop.

Leo is Amanda's former best friend who shares her exact birthday. He struggles with his own insecurities and a desire to fit in with the popular boys at school, which causes him to make hurtful comments that sever his oldest friendship. Like Amanda, he finds himself trapped reliving the same Friday over and over.

Angelina is an eccentric older woman who has lived in Willow Falls for as long as anyone can remember. She wears a distinct duck-shaped birthmark on her cheek and works various jobs around town, including driving the school bus and staffing the historical society. She harbors a mysterious awareness of the magic affecting Amanda and Leo.

Stephanie is Amanda's current best friend. She supports Amanda but also focuses on ascending the middle school social ladder. Her eagerness to join the gymnastics team and associate with popular girls creates tension and insecurity for Amanda.

Kylie is Amanda's thirteen-year-old older sister. She deals with her own teenage anxieties, particularly concerning boys and her physical appearance. She frequently dismisses Amanda's concerns and unintentionally contributes to the stressful events of Amanda's birthday morning.

Mrs. Ellerby is Amanda and Kylie's mother. She works a demanding job and accidentally takes the wrong presentation poster to work on the morning of Amanda's birthday, an error that causes her significant professional trouble. She tries to support Amanda through the conflict with Leo but struggles to manage her own stress.

Mr. Ellerby is Amanda and Kylie's father. He spends Amanda's eleventh birthday suffering from a severe cold on the couch. Despite his illness, he tries to offer his daughter comfort regarding her ongoing rift with Leo.

Ruby is a popular girl in the fifth grade who successfully makes the gymnastics team. She can be snide and intimidating, representing the exclusive social circles that Amanda both resents and desperately wishes to join.

Mrs. Fitzpatrick is Leo's mother. She enforces the shared birthday tradition for years and remains a supportive presence in Leo's life, though Leo sometimes feels pressured by her social expectations regarding Amanda.

Mr. Fitzpatrick is Leo's father. He attends the joint birthday celebrations and expresses excitement when Amanda finally calls the house after the children's long period of silence.

Mrs. Grayson is a neighbor of the Ellerby family. She drives Amanda to the doctor during one of the repeated days and possesses deep historical knowledge about the long-standing feud between the prominent families in Willow Falls.

Tracy is Emma's twin sister and one of Amanda's loyal friends. She helps present Amanda with a birthday cupcake at lunch, providing a steady presence that Amanda initially takes for granted.

Emma is Tracy's twin sister. She forms part of Amanda's core friend group at school, offering support and celebration that Amanda struggles to appreciate amidst her ongoing drama with Leo.

Vinnie is a boy at school who bullies Leo. His intimidating presence heavily influences Leo's self-conscious behavior and his desperation to appear cool to his peers, which ultimately damages Leo's friendship with Amanda.

Mr. McAllister is the owner of the local party venue who hosts the first shared birthday party for Amanda and Leo. He shares a knowing look with Angelina, suggesting his involvement in establishing the children's lifelong tradition.

Leonard Fitzpatrick is Leo's great-great-grandfather. He was a Willow Falls resident whose long-standing enmity with the Ellerby family remains an infamous piece of local history.

Ellerby is Amanda's great-great-grandfather. He was a farmer in Willow Falls who engaged in a notorious, bitter feud with the neighboring Fitzpatrick family.

Dustin is a classmate of Kylie's. He spends time studying at the Ellerby home, causing Kylie significant anxiety as she harbors a secret crush on him and worries about her appearance in his presence.