Ai Ninomiya, a 17-year-old Yumegaoka High School student and dedicated Diving Club member, shares her passion for diving with her twin brother, Makoto. Her striking appearance features pale skin, vivid green eyes, and thick pinkish-red hair styled into two spiky pigtails, secured with three bobby pins to tame her bangs. Humidity or rain demands extra pins to combat frizz, while her gradually lengthening locks now curl into subtle waves at the tips.

Energetic and hot-blooded, Ai vents frustrations through physical humor—often kicking Makoto—yet fiercely protects him despite these outbursts. Her mornings crawl through three groggy hours due to hypotension, and indecision often slows her choices. Beyond her fiery exterior, she balances tenderness with responsibility, mentoring juniors Hikari Kohinata and Futaba Ooki with a blend of guidance and warmth.

As a Diving Club upperclassman, Ai’s dynamic presence fuels both camaraderie and growth among peers. Her spirited clashes with Makoto inject levity, contrasting moments where her maturity shines, revealing layers beneath the chaos—a sempai who nurtures as fiercely as she teases, embodying the club’s spirited heart.