Yumi is the older child of Kasumi Shimizu, therefore she is the first in line of taking over the Ryokan Hiei. However, Yumi had no interest of taking over the inn and prefers the city life. Her relationship with her family soon soured and as soon as she was old enough, she bought an apartment in the city of Kyoto and moved out.
Some time later, her mother Kasumi drowned in one of the ryokan's baths. Miwako blamed Yumi for their mother's death and the relationship between the sisters became strained.
During Nancy Drew's investigation of the haunting of the ryokan, Yumi can get defensive when Nancy asks about her family and at one point, orders her to leave.