Shizuha Doi is a 16-year-old candidate pilot training at Shimoji Airbase. As the daughter of a professional photographer, she lacks her father's extroverted traits, finds his behavior occasionally embarrassing, and exhibits none of his perceived intrusiveness. Her surname translates to "earth" in English.

Studious and ambitious, Shizuha stands as the most compliant member of her social group, maintaining a balanced and level-headed disposition. She contrasts sharply with her peers—less temperamental than Ayamo Nakamura, less apathetic than Karin Kikuhara, and less chaotic than Mikaze Honjou. Despite her cautious nature, Shizuha frequently gets pulled into risky situations by her roommate and close friend Mikaze due to her inability to refuse requests.

Her responsibilities include serving as Mikaze's automatic alarm system for classes and discreetly attempting to prevent Mikaze's daydreaming during training sessions, though these interventions rarely succeed. Shizuha shares the aspiration to become a Comet Blaster and travel to space but pursues this goal with less intensity than Ayamo or Mikaze.

She holds multiple licenses and certifications reflecting hidden talents beyond piloting, including cooking abilities and a Universal Driver's Licence that implies broad operational competence. Across the series, her character evolves into a deadpan snarker. During dangerous scenarios instigated by her friends, Shizuha demonstrates calm and composed problem-solving.