Kasane Tōdō, the youngest of the three Tōdō sisters with older siblings Tsumugi and Koyori, attends middle school in the rural town of Yamabiko. She shares a classroom and close friendship with Ayumu Hoshino, the protagonist's younger brother. Physically distinctive, Kasane has light blue hair swept to the side with a half-moon clip and amber eyes. At 142 cm, she stands as the series' shortest character. Her typical attire is a sailor-style school uniform, occasionally paired with thigh-high stockings and a ribbon tie.

Cheerful, energetic, playful, and carefree, Kasane garners the nickname "Fast ears" across Yamabiko for her enthusiastic pursuit of local rumors and gossip. Despite this trait, she remains friendly, insightful, and observant, readily sharing gathered information. Her demeanor reflects the family's characteristic fearlessness and attentiveness.

Kasane maintains a typical sibling relationship with her sisters, viewing them with admiration. Her well-documented friendship with Ayumu Hoshino involves frequent school interactions but stays platonic due to her age and middle school status. Though she expresses a general preference for older boys, no romantic storylines feature her in official media, as she is not a romanceable character in the original visual novel or adaptations.

Across the anime, visual novels, and supplementary materials like the fan disc "Hoshizora e Kakaru Hashi AA," Kasane exhibits no significant character development or expanded backstory beyond these traits and connections. She consistently functions as a supportive secondary figure, contributing to the slice-of-life tone through her interactions and lighthearted subplots.