Mai lives in Higashi Osaka with her father, mother, and older brother. Prone to unexplained fevers, she often misses school, but she returns on the eighth day of the new semester, and becomes caretaker of the class rabbit, Sumi-chan.

When the class rabbit escapes, Mai runs around searching for it and comes down with a fever. The doctor suggests she change her living environment. Megumi hesitates when Kota suggests taking Mai to her estranged mother, Shoko.

Mai's father sends her and her mother to the Goto Islands. At the ferry port, they meet Megumi's mother. It is Mai's first time meeting her quiet, stern-looking grandmother. In her mother's childhood home, Mai sees a new side of her mum.

On Mai's first day at her grandmother's house, shipwright Kido and portside shop owner Sakura drop by. When Megumi returns from the clinic, she sees Mai excitedly touching an octopus Sakura brought and scolds her.

Encouraged by her grandmother, Mai tells her mother she wants to join the school's seaside outing. Megumi agrees but remains anxious. As Mai tries to get out of the water, she falls and gets hurt.

With Megumi back in Higashi Osaka, Mai begins living with Shoko, who teaches her to be independent and try new things. When Mai struggles, Shoko encourages her.