Sayomi Hanawa, Kaoru Hanawa's older sister, is a university student living outside Takehara who returns home during holidays. Her well-meaning but flighty personality drives her to organize lengthy excursions seeking secluded scenic spots, frequently dragging along reluctant companions like her sister and friends. These trips yield memorable experiences despite notorious arduous hikes and Sayomi's anxiety-inducing driving. She possesses a knack for nicknaming, having coined Fuu Sawatari's enduring childhood nickname "Potte."

"Her connection to the group intensifies upon learning of Fuu's quest to find locations from her late father's photographs. Sayomi proactively assists, leveraging self-proclaimed local knowledge to lead expeditions targeting these meaningful sites. Though her navigation skills often trigger unexpected detours that prevent reaching intended destinations, the journeys foster bonding and create new cherished memories.

During the graduation film arc, Sayomi maintains her supportive role. She appears at significant events like the Kaguya-hime Parade, where her "Mini-Sanctuary Explorers Club" activities involve characters such as Kanae Mitani in fortune-telling booths, highlighting her ongoing enthusiasm for crafting unique experiences. Her presence throughout Fuu's final high school year and graduation underscores continued involvement in the group's milestones.