Akari Mizunashi hails from Japan on Manhome (Earth) and immigrated to the terraformed planet Aqua (formerly Mars) at age fifteen. Her goal was to train as an Undine, a professional gondolier and tour guide in Neo-Venezia. She became an apprentice Pair at Aria Company under Alicia Florence, one of Neo-Venezia's elite "Three Water Fairies." Akari possesses spring green eyes and cherry blossom pink hair, typically worn in two long side ponytails secured by yellow clasps with straight-cut bangs. Her hair grows longer in adulthood. She wears Aria Company's seasonal uniforms: a summer version with a cropped blouse, ankle-length dress, blue-and-yellow accents, and white boots; and a winter variant featuring a cape, long sleeves, grey tights, blue-and-yellow accents, and white boots.

Akari's defining characteristic is her profound appreciation for everyday experiences, frequently discovering wonder in mundane or overlooked aspects of life. Her peers term this perspective the "Akari filter," enabling her to perceive and highlight beauty in ordinary moments. Her cheerful demeanor, frequent use of expressions like "hahii" and "hohee," and infectious positivity allow her to form effortless connections with strangers, gradually making her a well-known figure in Neo-Venezia. Though often perceived as airheaded or easily distracted due to her dreamy disposition, this outlook stems from a deliberate choice to embrace joy and curiosity. Alicia Florence likened her to "pure white snow," reflecting the world's subtlest colors and uncovering infinite wonder. Observations suggest her optimism may conceal an unspoken past, adding complexity.

Her professional development shows incremental growth. Initially, she struggled with rowing due to learning backward techniques on Earth-based simulators, though this later became a unique skill. She advanced from Pair to Single after eleven months, demonstrating improved technical competence and deepening relationships with fellow trainees Aika S. Granzchesta and Alice Carroll. Her journey culminated in passing the Prima exam under Alicia, earning the title "Aquamarine" (Harukanaru Ao, or "Distant Blue"). This progression parallels her emotional maturation, particularly in navigating Alicia's retirement and marriage, which she accepted with grace while carrying forward her mentor's philosophy.

As a Prima, Akari mentors new trainees like Ai, emphasizing the principles of finding joy in work and life that defined her own training. Her influence extends beyond technical guidance; she inspires others to reexamine Neo-Venezia's beauty through her perspective. Later appearances reinforce her role as a stabilizing presence within Aria Company and the broader Undine community, maintaining her signature warmth while embodying the responsibilities of a senior Undine.