Wren is a highly organized, practically minded professional working in finance who has returned to her childhood home in the Great Plains. Her routine is predictable and managed, offering her a sense of safety and stability that contrasts with her difficult upbringing. Emotionally reserved, she is deeply challenged when her husband receives a life-altering diagnosis that forces her to adapt to circumstances entirely outside her control.

Lewis is a romantically minded high-school theater teacher who moved back to Texas after struggling to launch an acting career in New York City. He views living as an art form and approaches life with a theatrical, daydreaming sensibility. When he receives a diagnosis of a rapidly progressing mutation, he attempts to process his changing reality through playwriting and his enduring love for his wife.

Angela grows up in a dysfunctional household with an absent father and a mother struggling with alcohol addiction. Seeking validation and care outside her home, she matures quickly and relies on an evolving support network of friends and romantic partners. Her life is profoundly shaped by an early pregnancy and a subsequent medical diagnosis that alters her family dynamic forever.

Margaret is a former human who was diagnosed with a mutation as a child. She insists on using her full name as a way to hold onto the memory of her parents. Despite her circumstances, she maintains an ebullient, youthful energy and a deep optimism about finding a community in her new environment.

Tiny Pregnant Woman is a former high-level competitive swimmer who intentionally ended her athletic career. She returns to the water while managing a high-risk pregnancy, as her twins have developed a mutation in the womb. She forms a bond with Wren over their shared experiences with incurable conditions and anticipatory grief.

Marcos is an older youth who lives on a houseboat and makes money by selling off its parts. He initially provides the teenage Angela with the attention and validation she lacks at home. However, his charm masks a highly controlling nature, leading to a volatile and increasingly dangerous dynamic.

Julia is a Chickasaw woman who becomes a fast friend to Angela when they work together at a local motel. She is fiercely protective and observant, standing up to judgmental guests and actively intervening when she notices signs of trouble in Angela's personal life.

George is Julia's brother, a dependable and caring young man who quickly becomes a fixture in Angela's life. He provides safe transportation, thoughtful gestures, and steady support, standing in contrast to the other men Angela has known.

Theresa is Julia and George's mother, a matriarch within the Chickasaw community. She immediately extends her protective, maternal instincts to Angela, offering her food, shelter, and a non-judgmental environment when she needs it most.

Colleen is Angela's mother, a woman struggling deeply with alcohol addiction. Her illness prevents her from being a present or effective parent, leading to a strained household dynamic and forcing her daughter to seek emotional support elsewhere.

Rachel is a doctoral candidate who becomes Wren's first serious romantic partner. She is comfortable with the fundamentally unknowable nature of her academic field, which fascinates the highly practical Wren.

Pierce Anthony is an inexperienced television drama enthusiast hired to replace Lewis as the school's theater teacher. His approach to directing the annual production deeply offends Lewis's theatrical sensibilities.

Greg is Lewis's father. He and his wife serve as a foundational support system for Lewis and Wren as they navigate the devastating reality of Lewis's medical diagnosis.

Annie is Lewis's mother, a caring woman who initially assumes her son's big announcement will be about having a baby. She is deeply shocked by the reality of his mutation but remains a loving presence in his life.