Chisaki Hiradaira is a gentle and kind-hearted girl raised in the undersea village of Shioshishio. She is characterized by her long, deep bluish-purple hair that reaches her waist and clear blue eyes, possessing a slender and refined aura. Five years later, she cuts her hair to shoulder length and matures into a composed adult woman, though her gentle smile and soft atmosphere remain unchanged.

Her personality is deeply compassionate and nurturing, making it impossible for her to ignore someone in trouble. On the other hand, she has a delicate side where she bottles up her own feelings and endures in silence to avoid hurting others. While she is a responsible pillar of support for her friends, she tends to internalize her worries. In romance, she is devoted and sincere but extremely shy, struggling to express her feelings honestly. Nevertheless, she is a person of both kindness and inner strength who can act courageously for the sake of those she holds dear.

The type to wear his heart on his sleeve and speak his mind. He will act recklessly for the sake of those he loves. He harbors strong romantic feelings for Manaka, which often manifest in his actions. Usually blunt and foul-mouthed but deeply cares for his friends. He is particularly jealous regarding Manaka and gets emotional when she is close to other boys, often speaking harshly to hide his embarrassment.

A girl who is gentle, a bit airheaded, and slightly unreliable, yet possesses a charm that draws people in. She is sensitive to others' emotions and has a kindness that won't let her leave a grieving person alone. She is dense when it comes to romance and is the type to be late in realizing her own feelings. She calls Hikari "Hi-kun" and Chisaki "Chi-chan."