Hiwako Funabashi is a secondary student at the same high school as the main character, Makoto Saeki. She is a model student who holds the position of student council vice president. Hiwako comes from a highly prestigious and wealthy family; her family specializes in the traditional tea ceremony, and her father is a member of the National Diet, the Japanese legislature.

Initially, Hiwako presents herself as being cold, stern, and somewhat aloof towards her peers. Her strict and formal upbringing is the primary reason for this distant demeanor, as she was raised to uphold certain standards of behavior and social expectation. This manifests in her interactions at school, where she can be seen as bossy or overly critical, such as when she scolds a classmate for talking out of turn in physical education class. Despite her composed exterior, there is a sense that she is not entirely comfortable with the rigid persona she has adopted, appearing almost sad or reluctant to behave in such a way, though she believes it is necessary. Underneath this formality, she is shown to have a genuine and caring nature that emerges once she becomes more comfortable with others.

Her primary motivation evolves from maintaining her family's expectations and social standing to seeking personal happiness and authentic connection. Her journey in the story begins when she encounters Makoto and another classmate, Yumi Ikegami. While Hiwako and Yumi initially clash due to their contrasting personalities, they eventually develop a close friendship. Through this friendship, Hiwako begins to change, becoming noticeably warmer, more open, and visibly happier than before. Her role in the narrative is largely centered on this personal growth and her interactions within the main trio of friends. One episode focuses on her desire to find a birthday present for her often-absent father, showcasing her family dynamics and affections.

Her key relationships include her close bonds with Makoto and Yumi, who accept her for who she is and help her break out of her shell. She also shares a complex relationship with her family, including a mother whom she stands up to and a father she clearly cares for despite his frequent absence. A notable running thread is her apparent romantic interest in older men, specifically Makoto’s father, Tatsuo Saeki, and a hinted-at mutual attraction with her father's much older assistant, Yoshizumi. Her development is significant, as she transitions from a rigid and isolated individual to a more relaxed and emotionally open young woman who learns to express herself and enjoy her youth. While she has no supernatural abilities like the series' main character, her notable strengths lie in her intelligence, leadership as student council vice president, and her strong will, which is demonstrated when she defies her mother's wishes to live more authentically.