Izumi Chiba, a middle school student from Kumamoto Prefecture, lives above her family's fruit and vegetable shop with her parents, Shigezo and Sayuri Chiba.

Her outgoing nature emerges when she meets Natsuna Keyaki, who is searching Kumamoto for her missing friend, Itsuki Kusunoki. Izumi immediately joins the search, introducing Natsuna to her friends and organizing activities like watermelon-smashing—where Natsuna accidentally falls into a canal.

Izumi brings the soaked Natsuna home, offering dry clothes and support. During this visit, Izumi shares a personal secret: her romantic feelings for local police constable Masayoshi Maezono, deepening their new friendship.

Izumi actively aids the investigation. Examining a landscape painting from a local candy store owner, she spots Itsuki Kusunoki's signature, confirming the artist. Later, her mother identifies the painted location as Sakitsu, a fishing village in the Amakusa region.

Izumi has brown hair styled in shoulder-length braids and yellow eyes, typically seen in her school uniform.

When Natsuna departs Kumamoto, Izumi becomes emotional. She tearfully hugs Natsuna goodbye at the airport, underscoring the bond formed during the visit.