Hamamoto is a female child character with neck-length orange or brown hair and green eyes. Intelligent and sharing Aoyama's strong interest in scientific investigation, she actively researches the mysterious penguin appearances and the floating forest water sphere she names "the sea." She leads Aoyama and Uchida to this sphere for observations and experiments.

Her father, a meteorological researcher, later studies the sphere phenomenon after reading about it in her journal. When the sphere expands dangerously and her father disappears, rescue efforts commence.

Hamamoto harbors romantic feelings for Aoyama, manifesting as jealousy toward his close relationship with the Lady. This jealousy prompts pointed remarks about Aoyama's motivations. She interacts with classmate and bully Suzuki, who has a crush on her; she confronts him upon his discovery of the sphere's location, demanding secrecy.

Throughout the investigation into the penguins and the sphere, Hamamoto collaborates closely with Aoyama and Uchida, contributing to their collective scientific efforts. Her consistent role is a supporting character focused on solving these central mysteries alongside her classmates.