Chisaki Hiradaira

A calm and compassionate 14-year-old middle school student from Shioshishio, a village located in the sea. Chisaki is the childhood friend of Manaka, Hikari, and Kaname, and together they attend Mihama Junior High School, which is located in the surface town of Oshiooshi. She attempts to act mature in most situations, putting her friends' feelings before her own, but her temper can flare up whenever she gets especially frustrated - in particular towards Tsumugu, whose new presence she believes is spoiling the harmonious relationship between her friends.

Chisaki harbors an unrequited crush on Hikari, although he is unaware of her feelings. She also has a complex about her body​ and hates change to the point where it hinders her own emotional development.