Joshua is a medical device engineer in his twenties living in Providence, Rhode Island. Diagnosed with autism in childhood, he manages intense emotional spikes with verbal exercises and physical activity. He prefers a reclusive lifestyle, focusing heavily on his highly successful engineering career. Following his wife's terminal diagnosis, he faces severe grief and must learn to accept support from his community.

Lauren works as an architect designing public spaces in Providence. She receives a terminal diagnosis of idiopathic pulmonary fibrosis shortly after her wedding. Rather than succumbing to despair, she focuses on living fully in her remaining time and preparing those she loves for her absence. She organizes a series of monthly letters for her husband to read over his first year without her.

Sarah works as a social worker for the Department of Children, Youth, and Families. She has been Lauren's best friend since childhood. She takes on the responsibility of hand-delivering posthumous letters each month. She carries some long-standing jealousy regarding her friend's successes but remains fiercely loyal during her illness.

Radley works as a salesperson at a mall clothing store while taking part-time classes to become a licensed therapist. Originally from rural Maine, he moves to the city after coming out to unsupportive parents. He quickly becomes a compassionate confidant for Joshua, helping him with practical tasks and emotional hurdles.

Jen is Lauren's older sister. She lives locally with her husband, Darius, and their two young children, Sebastian and Octavia. She is open about her sadness regarding her sister's declining health and cries freely with her family. She provides a warm, welcoming presence for her brother-in-law.

Ben is a Korean Buddhist who lives next door to Joshua's childhood home. He acts as a surrogate father, offering quiet support and guidance. He possesses a calm demeanor that effectively diffuses tension during stressful moments, preferring companionable silence over unsolicited advice.

Stephanie is Joshua's mother. She raised her son independently in Rhode Island after her partner abandoned her during her pregnancy. She maintains a close relationship with the Kims, who live next door and provide a built-in support network.

Donna is a retired teacher and the mother of Lauren and Jen. Widowed when her husband passed away, she struggles to process her younger daughter's illness and often centers her own grief in conversations. She eventually finds comfort in dating a man from her support group.

Dave is Lauren and Jen's father, who passed away from an aneurysm while Lauren was in college. His sudden death profoundly impacted his family and inspired his younger daughter to change her career path. He serves as the silent recipient of private letters written by his daughter.

Rose is a waitress living in the Providence area. She owns a sixteen-year-old dog named Duffy and has a brother with a joint syndrome. She crosses paths with Joshua early in the story and continues to appear in his life through chance encounters.

Christopher is a tenured engineering professor at a university in Chicago. He dated a woman from Harvard during his college years but abandoned her upon learning of her pregnancy. He built a completely separate life and family in the Midwest, hiding his past from his current relatives.

Darius is married to Jen and helps raise their two young children. He actively includes his brother-in-law in family activities, such as community 5K runs, to ensure he does not isolate himself from the family.

Dr. Bennett is a pulmonologist working at Rhode Island Hospital. She diagnoses her young patient with idiopathic pulmonary fibrosis and oversees the difficult palliative care process, remaining honest about the lack of a cure.

Bruce manages the architectural firm where Lauren works. He transitions from a traditional employer to a highly supportive friend as her illness progresses, allowing her flexibility in her schedule and installing a bed in her office so she can rest.

Sumi is married to Ben and lives next door to Stephanie. She is deeply involved in her community and frequently shares meals with her neighbors, offering constant, cheerful support to those around her.

Pebbles is a pet dog brought into the Park household. She is specifically trained and cared for to ensure she can provide necessary companionship and a daily routine for her owner's husband after a terminal illness runs its course.

Charlotte lives on the first floor of the apartment building. Often referred to as "Creepy" Charlotte, she makes awkward and poorly timed flirtatious comments to her grieving neighbor in the hallways.

Cammie is a consensual sex worker who hopes to open her own bar and salon called Shine. She meets a grieving widower for a date and shows genuine empathy for his unique situation, choosing kindness over a purely transactional encounter.

Gertie is a local medium who refuses to charge a fee for her services. She relays specific signs and messages about the afterlife, providing profound comfort and startling accuracy to grieving clients.

Lori works at the same architectural firm as Lauren. She lacks empathy for her coworker's declining health, eager to take over her office and filing formal complaints about the accommodations made for sick employees.

Asmaa directs the Hope Center in Providence. She oversees the volunteers and coordinates the facility's design renovations, working closely with local architects to improve the space.