Mark is a twelve-year-old boy who has battled cancer intermittently since age five. Following news that his illness has returned, he runs away from home to climb Mount Rainier. He carries a camera to document his existence and copes with uncertainty by writing five-seven-five syllable haikus. His fierce desire for independence often masks his fear of dying and his frustration over a life dictated by medical treatments.

Jessica is Mark’s steadfast best friend from early childhood. She shares his love for haiku poetry and possesses a deep understanding of his inner struggles. While Mark travels alone, she remains at home holding the secret of his true destination. She constantly weighs the ethics of keeping her promise against her desire to keep him safe.

Beau is a faithful mutt with black and brown fur and mismatched eyes. He accompanies Mark on his grueling journey toward the mountain. He operates entirely on instinct and affection, ignoring his own hunger and fatigue to stay close to his owner. His presence offers Mark vital physical protection and quiet comfort.

Mark's mother and father are emotionally exhausted from years of managing their son's illness. His father processes the disappearance with intense quiet, often staring blankly at newspapers. His mother cries silently but maintains the household routine and insists her husband eat. They rely on the police hotline and Jessica's company while waiting for updates.

Shelby is a six-year-old girl with curly red hair traveling to Elbe. She is visiting her father's new house for the first time since her parents divorced. She feels betrayed and plans to give her father the silent treatment, prompting Mark to evaluate his own feelings of anger.

Wesley is a park service biologist working near Mount Rainier. He drives a green truck and wears a white cowboy hat. He sports a mustache and smells of cigars. He carries the grief of losing a son in the military, and when he suspects Mark's true identity, he uses conversation rather than force to understand the boy's motivations.

The waitress works a late shift and wears heavy makeup to cover a black eye. She serves Mark and Beau their food while constantly chewing gum. When she realizes Mark is sick in the bathroom, she attempts to show him mercy, though her unsolicited sympathy triggers his frustration.

Mark's grandfather was an avid mountain climber who died slowly of kidney disease. He gave Mark his vintage camera and a pocket watch. His final weeks in the hospital deeply affected Mark, who views his grandfather's lingering death as exactly the fate he wishes to avoid.

The shuttle driver operates a transport vehicle heading up the mountain. He grows visibly irritated when he discovers an unpaid passenger hiding on board. His cold demeanor contrasts sharply with the hospitality the boy occasionally encounters elsewhere.

Jessica's mother shares custody of her daughter following a divorce. She works late shifts, leaving Jessica to frequently eat dinner with Mark's parents. She notices her daughter's intense grief and allows her to skip school while the search continues.