Koharu Shirahane is the younger sister of Yukina Shirahane and the daughter of Takehito Shirahane and Hiromi Shirahane. She is a third-year elementary school student, living with Yukina at their uncle's temple. Koharu enjoys watching historical dramas on television, which reflects her curious nature and interest in stories from the past. In the narrative, she provides emotional support to her sister and represents the ordinary family life that the main characters strive to protect. She adapts to the extraordinary events around her with youthful curiosity and interacts warmly with Kennosuke Tokisada Ouma, the samurai from the past. While she does not participate in combat or technical operations, her presence grounds the story in a sense of normalcy. Her relationship with Yukina is close and affectionate, and she maintains a loving bond with her parents despite living apart. Throughout the series, Koharu remains a steady, supportive figure within the family, embodying the everyday life that is at the heart of the conflict.