Scarlett is a twenty-one-year-old premed student and Division I diver at Stanford University. A severe injury during her freshman year NCAA championships left her with a persistent mental block, specifically concerning her inward dive. She operates as a highly organized, goal-oriented student who worries constantly about academic and athletic failure. Outside of her studies and sport, she harbors a private interest in BDSM that she has struggled to communicate in past relationships.

Lukas is a Swedish Olympic swimming champion competing for Stanford University. He projects a quiet confidence and maintains an impeccably clean apartment, utilizing strict discipline to manage his life following the death of his mother during his teenage years. As a premed student, he works alongside Scarlett on a biology research project, where their academic connection naturally transitions into a physical one based on mutual trust and specific sexual preferences.

Penelope, universally called Pen, serves as the outgoing and popular captain of the Stanford diving team. She establishes easy connections with her peers and acts as Scarlett's synchronized diving partner. Following a realization that she and her longtime boyfriend lack sexual compatibility, she ends their relationship to explore her independence, though she remains emotionally attached to him.

Sam is a therapist working in Stanford's Counseling Services department. She possesses a neutral, composed demeanor and frequently wears beige clothing. Lacking specific knowledge about competitive diving, she relies on direct, challenging questions to help her clients articulate their fears.

Barb is a medical doctor living in St. Louis and Scarlett's stepmother. Years earlier, she separated from Scarlett's abusive biological father, taking Scarlett with her to provide a safe environment. She serves as a steady, reliable parental figure and the inspiration for Scarlett's premed aspirations.

Alex is Scarlett's estranged biological father. His past abusive behavior necessitated a restraining order and heavily influenced Scarlett's deep-seated anxieties regarding control and failure.

Josh is Scarlett's ex-boyfriend. His sudden decision to end their relationship over the phone on the day of a major diving competition contributed heavily to Scarlett's ensuing mental block.

Coach Sima leads the Stanford diving program. He oversees the team's daily practices, makes strategic decisions regarding synchronized pairings, and monitors the physical and mental recovery of his athletes.

Maryam is Scarlett's college roommate at Stanford. She provides grounded advice and encouragement when Scarlett struggles with difficult classes or feels overwhelmed by medical school applications.

Theo is a former teaching assistant at Stanford University. He begins a romantic relationship with Penelope after her highly publicized breakup with Lukas.

Bree is a diver on the Stanford team. She socializes frequently with the team captain and co-hosts large parties for her fellow student-athletes.

Bella is a member of the Stanford diving team. She shares a tight-knit social circle with Penelope and Bree, frequently organizing events for the group.

Victoria is Penelope's original synchronized diving partner on the Stanford team. An early-season injury forces her to step away from active competition, prompting roster changes.

Zach is a graduate student in the biology department. He coordinates the daily operations of Dr. Smith's research project and interacts regularly with the undergraduate assistants.

Jan is Lukas's brother who visits from out of town. He possesses deep insight into his sibling's long-standing habits regarding discipline, offering an external perspective on Lukas's personality.

Hasan is Lukas's college roommate. He maintains a good-humored attitude about his roommate's intense cleaning habits and strict routines.

Kyle is a swimmer on the Stanford team and one of Lukas's athletic friends. He expresses surprise when seeing his high-profile teammate socialize outside their usual circles.

Hunter is a fellow swimmer who spends time with Lukas outside of practice hours. He forms part of the core swimming team social group.

Carissa is a competitive diver whom Scarlett originally met on a recruiting trip to Florida. She harbors deep animosity toward Penelope originating from a conflict at their shared childhood swim club in New Jersey.

Dr. Carlsen is a biology professor at Stanford. He recognizes Scarlett's academic talent on written assignments and recommends her for a specialized research position to boost her medical school applications.

Dr. Smith is a faculty member leading a biology research project. He employs several undergraduate and graduate students to assist with data mapping and laboratory work.

Mr. Kumar is Scarlett's former high school diving coach. His unexpected presence at the aquatic center triggers intense performance anxiety for Scarlett, causing her to flee the event.