Sam is a popular high school senior who initially believes her social status shields her from consequences. She spends her days focusing on teenage insecurities, planning to lose her virginity to her boyfriend, and participating in the bullying of less popular classmates. When she becomes trapped in a time loop reliving February 12th, she is forced to confront her choices and behavior. She slowly learns to prioritize the needs of others over her own desires.

Lindsay is Sam's best friend and the unspoken ringleader of their popular clique at Thomas Jefferson High. She is a reckless driver who projects high confidence but rarely apologizes for her misdeeds. Behind her aggressive exterior and tendency to verbally attack others, she carries deep emotional baggage stemming from her parents' divorce during her elementary school years.

A slightly awkward teenager who was good friends with Sam during their childhood. Sam distanced herself from him when she became popular, but he continues to hold strong feelings for her. He consistently demonstrates genuine kindness and care, standing in stark contrast to the superficial relationships in Sam's life.

An outcast student dubbed "Psycho Killer" by the popular clique. She is the constant target of severe bullying, primarily led by her former childhood best friend, Lindsay. The unrelenting harassment has pushed her to a breaking point, making her a crucial catalyst in the events of Cupid Day.

One of Sam's close friends and a core member of the popular clique. Her behavior is heavily influenced by the people around her, causing her to alternate between sensitivity and cruelty depending on Lindsay's actions. She often plays the peacemaker when tensions rise within their social circle.

A lively member of Sam's friend group who prioritizes social enjoyment. She is enthusiastic about parties, drinking, and having a good time. Beneath her energetic and sometimes promiscuous exterior, she possesses a gentle nature and primarily wants her friends to be happy.

Sam's younger sister. At first, Sam views her as a minor annoyance who gets peanut butter on her clothes and wakes her up too early. Despite her young age, Izzy possesses a strong sense of self and refuses to bow to peer pressure, holding onto a bravery that Sam slowly begins to admire.

Sam's boyfriend, whom she has idolized since the sixth grade. They have been dating for a few months, and he is eager to take their relationship to a physical level. He focuses heavily on his own desires and social standing, showing little genuine concern for Sam's emotional well-being.

The twenty-five-year-old math teacher at Thomas Jefferson High. He engages in highly inappropriate flirtation with his teenage students, providing Sam with a false sense of validation and power before she eventually sets boundaries with him.

A student at Thomas Jefferson High who struggles in chemistry. She is the classmate Sam cheats off of to protect her chances of getting into Boston University.

A socially marginalized student who wears combat boots and has cruel graffiti written about her on the bathroom stalls. She questions why the popular girls are so mean and harbors secrets regarding her romantic life.

The strict assistant principal at Thomas Jefferson High, known among the students as the "Nic Nazi." Despite her harsh disciplinary exterior, she hides a personal relationship with another faculty member.

The gym teacher at Thomas Jefferson High. He is secretly engaged in a romantic relationship with the assistant principal, which Sam accidentally discovers while hiding.

A male student at the high school who maintains a public relationship while secretly carrying on an affair with Anna Cartullo.

A student at Thomas Jefferson High who is dating Alex, completely unaware of his infidelity until tensions boil over at a party.

Juliet's younger sister. She is innocent of the high school drama and thoroughly confused by the cryptic warnings Sam tries to pass along to her older sister.

The mother of Sam and Izzy. She tries to connect with her teenage daughter, though Sam often shuts her out or takes advantage of her trust, such as by stealing her credit card for a shopping spree.

The father of Sam and Izzy. He attempts to enforce household rules and parenting standards, leading to typical teenage friction with his oldest daughter.

Juliet and Marian's mother. She lives in a home that feels empty and unlived in, seemingly oblivious to the severity of Juliet's social isolation and torment.

The father of Juliet and Marian. He inhabits a quiet, gloomy household where the family photographs are never properly filled out.

The mother of Ally, whose house serves as a frequent gathering place for the friend group. She is the one who breaks tragic news to the girls during the repeating days.

A girl Sam and Lindsay went to school with. In the fourth grade, she was cruelly excluded from a dodgeball game due to her weight, a memory that haunts Sam in her final moments.

Lindsay's on-again, off-again boyfriend. Their volatile relationship is a constant topic of conversation among the friend group.