Belly is a teenage girl struggling to adjust to a summer at home after spending every previous summer of her life at the Fisher family's beach house. Deeply affected by the recent death of Susannah Fisher and a painful breakup with Conrad, she feels alienated from her high school peers. She is emotional and fiercely loyal, often preferring the comfort of her memories over engaging with her current reality.

Conrad is the elder Fisher brother and the object of Belly's longtime affection. He is quiet and stoic. He struggles immensely to express his feelings, often pushing people away to handle his pain internally. Following his mother's death, his profound grief causes him to abandon his summer college courses at Brown University, prompting a search to bring him back.

Jeremiah is the younger Fisher brother, known for his outgoing and friendly demeanor. He bore the heavy burden of being his mother's primary caretaker during her final days, an experience that matures him but also builds silent resentments. He harbors growing romantic feelings for Belly and wants to prove he is a reliable presence in her life.

Laurel is Belly and Steven's mother, and the late Susannah Fisher's best friend. She is a competent, practical woman who withdraws entirely into herself to cope with the loss of her closest companion. Her emotional distance creates friction with her daughter, though Laurel remains intensely protective of the Fisher boys.

Susannah is the late mother of Conrad and Jeremiah. She passes away from cancer prior to the start of the summer, leaving a massive void in the lives of her family and friends. Warm and glamorous, her spirit permeates the Cousins Beach house.

Adam Fisher is Conrad and Jeremiah's father and Susannah's widower. He carries the guilt of separating from his wife during her earlier illness before reconciling prior to her death. His pragmatic and emotionally detached approach to managing his grief puts him at intense odds with his children.

Steven is Belly's older brother. He shares the long history of spending summers at Cousins Beach with his sister and the Fisher brothers. While Belly and Jeremiah search for Conrad, Steven works a summer job and monitors the situation from afar.

Taylor is Belly's lively best friend from her hometown. She pushes Belly to participate in normal teenage activities and to move on from her heartbreak over Conrad. Her impatience with Belly's mourning process highlights the growing distance between the two friends.

Cory is a teenage boy from Belly's hometown who has a clear crush on her. He is somewhat awkward but well-meaning, though his flirtatious attempts fall flat with the grieving Belly.

Aubrey is Conrad Fisher's ex-girlfriend. Her presence at the Fisher home during a deeply vulnerable time causes intense jealousy and pain for Belly.

Sandy is the local real-estate agent hired to evaluate the Fisher property. She operates purely in a professional capacity and is unaware of the deep familial strife surrounding the house.

Mara is Jeremiah's former girlfriend. Their casual relationship ends when Jeremiah realizes he needs to devote his attention and energy to his ailing mother rather than a high school romance.

Nona is the hospice nurse employed to care for Susannah Fisher during her final decline. She provides necessary medical support while the family processes their impending loss.

Eric is Conrad's college roommate. He is unhelpful in locating Conrad and makes Belly uncomfortable by openly checking her out.

Nicole is a local girl who had a brief summer fling with Conrad the previous year. Her appearance at the house party forces Belly to assert herself and act as the property's hostess.

Maureen is the owner of a local hat shop in town. She is a friendly local who inadvertently forces Belly to voice the painful news of Susannah's passing.