Satsuki Toreishi is the third eldest of the five Toreishi siblings, aged 17 during the main story. She possesses dark violet hair, grey eyes, and blood type O. Piloting the agile air superiority fighter HB-03, comparable to a MiG-29 or Su-27 and optimized for close-range combat, she specializes in aggressive dogfighting tactics, contrasting with her eldest sister Kanna's interception style, though she occasionally coordinates directly with Yayoi. The HB-03's high maneuverability potentially exceeds an F/A-18 Hornet.

Satsuki suffers persistent insecurity about her appearance and flying capabilities, despite exhibiting exceptional piloting skills potentially unmatched in her squadron. She perceives herself as less physically developed than her younger sister Uzuki, particularly regarding breast size. During Hummingbirds musical performances, she participates in duets with the youngest sister, Mina, rather than solo stages.

The disappearance and presumed death of her father, fighter pilot Yuma Toreishi, whom she idolizes, during a flight mission deeply influences her emotional drive. Mentions of her missing father often motivate her to acts of notable bravery. Her piloting proved pivotal during the squadron's early encounter with rival group SNAP. Contractually bound to act as passive targets in a simulated engagement, Satsuki grew impatient with SNAP's inability to tag her aircraft despite her efforts. This culminated in her executing a daring nose-up midair stall in an F-14, a maneuver that led to her being tagged but showcased her advanced skills, drawing producer Shunsaku Kudou's attention and propelling the Hummingbirds into professional prominence.

Her family interactions include her mother Hazuki, who manages the team, and her grandfather Bun, the team's aircraft designer. Her father's absence remains a persistent influence.