Ayumi Futaba is a second-year junior high school student who lives in Miyagi Prefecture. She is the younger sister of Shotaro Futaba, the protagonist of the story, and maintains a close and positive relationship with him. Despite being a junior high student, she is still regarded as the baby of her family. Ayumi has brown eyes and shoulder-length brown hair.

In terms of personality, Ayumi is characterized as being detail-oriented, patient, and dedicated to supporting others. She is a loyal and conscientious individual who consistently prioritizes the needs of other people and places a high value on traditional family principles. Ayumi possesses strong observational skills and a good memory, which leads her to meticulously analyze her surroundings. She tends to avoid conflict, seeks stability, and shows hesitance when faced with new experiences or risks.

Ayumi's role in the narrative is primarily as a supportive family member. Her motivations are influenced by her caring nature and her family circumstances. Due to financial challenges experienced by her family, she works a part-time job alongside her academic studies, which results in persistent exhaustion. Despite this difficulty, she continues to persevere in pursuing her objectives.

Her key relationships center on her family, particularly her brother Shotaro, to whom she is very close and remains affectionate. She also shares a warm family bond with her mother, and she has a particular fondness for her mother's homemade gyoza dumplings. In group settings, such as at school, Ayumi naturally assumes a supportive role, offering motivation and emotional reassurance to her peers, which helps to strengthen group cohesion.