Caden is a 15-year-old talented artist who attends public high school. He struggles with schizoaffective disorder, experiencing severe anxiety, paranoia, and hallucinations that divide his reality. In his daily life, he faces a growing disconnect with his family and peers. Simultaneously, his mind constructs a vivid parallel world where he is a sailor on an old ship headed for the Marianas Trench.

Caden's mother and father are ordinary, well-meaning individuals who become increasingly alarmed by their son's erratic behavior, pacing, and paranoia. They attempt to intervene by taking him to therapists and eventually committing him to Seaview Memorial Hospital. Within Caden's fragmented perspective, they sometimes appear as helpless bystanders or masked entities with unknown intentions.

The Captain is a threatening and commanding figure who runs the ship in Caden's alternate reality. He wears a patch over a missing eye and alternates between wearing pirate garb and a woolen uniform. He demands absolute loyalty from the crew and actively tries to isolate Caden from the ship's other inhabitants, steering the vessel relentlessly toward Challenger Deep.

A teenager who serves as the map-maker on the ship and becomes Caden's roommate at the hospital. He creates complex navigational charts, mathematical formulas, and custom symbols to map out the world as he perceives it. He believes firmly in his own delusions and views himself and Caden as individuals channeling forces greater than themselves.

A teenage girl who appears in Caden's hospital life as a fellow patient and in his ship life as the wooden figurehead on the vessel's bow. At the hospital, she frequently stands by a large window, believing her observation keeps the outside world intact. She provides Caden with a crucial sense of empathy and companionship during his treatment.

Caden's primary psychiatrist in the hospital, who manifests on the ship as the Parrot. In reality, he wears bright Hawaiian shirts and has a glass eye. He diligently works to adjust Caden's medications and guide him toward recovery. In Caden's delusions, the Parrot is a scheming rival to the Captain who promises to help Caden escape the vessel.

A former hospital patient who now volunteers at Seaview Memorial Hospital, helping to facilitate group therapy sessions. In Caden's ship delusion, he appears as the swabby who cleans the decks. He manages his own schizoaffective disorder with medication and acts as a living example that recovery and stability are possible.

Caden's 11-year-old sister. She maintains a relatively normal childhood routine, playing video games and accompanying the family on trips, despite the growing tension in her household. Caden cares for her deeply and often uses thoughts of her safety as an anchor during his periods of intense anxiety.

A teenage patient at the hospital, identifiable by her blue hair. She frequently touches her nose to keep herself from feeling a sensation of falling. On the ship, she helps manage the crew's affairs. She provides Caden with small moments of interaction, including gifting him a puzzle piece of a blue sky.

One of Caden's high school friends. Max is knowledgeable about coding and handles the technical aspects of their video game project. As Caden's mental health declines and his conversation turns to bizarre concepts like out-of-body experiences, Max becomes visibly frightened and distances himself.

Caden's high school friend who writes stories for their shared video game project. She is perceptive enough to notice that Caden's artwork and behavior are declining. She initially assumes his erratic actions are due to drug use but attempts to offer him a listening ear, eventually visiting him in the hospital to apologize for her assumptions.