A shy girl who is good at cooking. She occasionally fishes at the shore, but she actually never catches anything. Her favorite food is Suika Bar (watermelon ice bars), and she often visits the candy store where Ao works to buy them. Her parents disappeared when she was young, and her only close relative is her grandfather, Kobato. Although she is a member of the youth group, she possesses a power to see the unhappy futures of those she gets too close to, so she tries to avoid interacting with others. She serves as a shrine maiden at the annual Summer Bird Ceremony. Kobato is a very intimidating person who often takes a domineering attitude. She is skilled at underwater martial arts.

A member of the youth group. A closet pervert with a bit of an overactive imagination. She speaks with a casual, feminine tone. Her favorite food is shaved ice. She works part-time at an old woman's candy store. At night, she patrols the mountains to guide the spirits of the dead known as Seven-Shadow Butterflies, but she doesn't talk to people about it much. Due to her own past recklessness, she caused an accident that left her twin sister, Ai, in a coma. To save Ai, she searches for her sister's soul among the Seven-Shadow Butterflies.

An energetic girl who always carries a suitcase. She absolutely refuses to show anyone what's inside, and when asked about her secrets, she says, "I'm not telling!" She visited this island once long ago and went on a secret treasure hunt with friends she met at a summer camp. She hid the locations of four keys as riddles and hid a treasure chest behind the school building. Inside, she placed a map to find a pirate ship—which, of course, isn't real, but she hid the fact that she made it herself.

An energetic girl living in the lighthouse who is always looking for things she wants to do. When she's surprised or at a loss for words, her catchphrase is "Mugyu." She loves cotton candy and spends her time picking up trash like Pringles cans. She is close friends with Shizuku and they are often together. She can only stay on the island during the summer and must leave when it ends, so she is currently searching for various things to do before then.

A girl who is a member of the youth group and is well-liked by her peers. Since Ryoichi Mitani occasionally strips naked on the island, she snipes and repels him with her self-made, high-powered water gun called the Hydro Gladiator. She shows no mercy to anyone who disturbs the public morals. Ryoichi is often seen with Tenzen, who loves table tennis.

An energetic little girl staying at Kyoko Misaki's house. She loves fried rice and is good at cooking it.

A refined and gentle woman. She is quite knowledgeable from reading old books while sorting through her grandmother's belongings in the warehouse. Even if you offer to help her organize, she politely declines. She is bad at cooking.

Umi's future self, and your future daughter.

Ao's twin sister. She loves Ao dearly and thinks Ao is the cutest person in the world.

Tsumugi's friend. She says the word "boobs" so often it makes you doubt your ears.