Hitomi Uehara serves as the younger sister of Koichi Uehara within the Uehara family. She initially displays intense disdain toward Coo, the kappa her brother introduces to their home, openly expressing discomfort and resisting the creature's presence. Her early interactions with Coo demonstrate visible reluctance and outright non-acceptance.

Gradually, Hitomi lowers her defenses and warms to Coo as she observes the kappa integrating into family life. Her initial resistance shifts into emotional attachment, reflected through evolving behavior that transitions from aversion to active engagement.

This relationship matures into notable affection, highlighting Hitomi's capacity for empathy and adaptability. Her character arc focuses on this progression from resistance to acceptance, ultimately forging a protective and caring bond with the kappa.