Fumitsuki Nanakorobi is a student who attends the same school as the protagonist, Chitose Hitotose. She serves as the class representative, a position that reflects her responsible and academically diligent nature. Fumitsuki is portrayed as a generally kind and gentle individual, though she possesses a somewhat surprising hidden strength or violent streak that can emerge in certain situations. Her primary motivation stems from her deep and intense romantic feelings for Chitose. She is genuinely curious about his private life, particularly the mysterious circumstances of his home where he lives with five of their female teachers who act as his surrogate mothers.

In the story, Fumitsuki acts as a catalyst for the central premise. Her curiosity about Chitose's home life creates a recurring threat to the secret arrangement the five teachers are trying to maintain, adding a layer of dramatic tension to the comedic narrative. Her role is that of a classmate with a romantic interest who is not in on the secret, placing her outside the central household dynamic but often bringing her into conflict or interaction with it. Key relationships for Fumitsuki are her one-sided romantic pursuit of Chitose and her connection to the five teachers, specifically her role as a student who must interact with them in a school setting while being unaware of their unconventional living situation. Her character sees some development, particularly as she becomes more deeply involved in the secrets of Chitose's life. One noted aspect of her involvement is her knowledge of a secret concerning Chitose, which she promises to keep. Fumitsuki does not possess any notable abilities beyond those of a typical honor student.