**Yukino Mizusawa** is the grandmother of Manaka and Ayaka Mizusawa. She runs the family-run hot spring inn, **Ryokan Shiki Ootoro**. This inn functions as both the family business and a central gathering hub for her granddaughters and their peers. Set to be inherited by Manaka and Ayaka upon their adulthood, the inn holds deep significance within the family. Yukino oversees its daily operations. Her presence anchors the familial foundation for the younger characters' activities and development, facilitated by the inn's role in hosting communal events and traditions.