Kasumi was the manager of the Ryokan Hiei and often wrote to her penpal, Maryanne. She lamented in her letters that she wished that her daughters would be closer. This may have been especially influenced by her absentee sister, whom their mother Takae notes did not even come for Kasumi's funeral.
When Kasumi was 42, she drowned in one of the baths in the ryokan. The family then blamed themselves for her death, since no one was with her because they had all grown so far apart. Nancy eventually learns from Takae that the night Kasumi died, she was going to see her friend Maryanne. Takae didn't like Maryanne because she always wound Kasumi up to leave the ryokan and see the world, so Takae pretended to be sick in order to prevent Kasumi from seeing her friend. It was Takae's job to clean the older of the two baths, a task she never before allowed Kasumi to handle since it can be very slippery, requiring knowledge of precisely where to walk. Kasumi slipped, possibly hitting her head, and ended up drowning.
After Kasumi's death, the ryokan started to attract rumors of being haunted by her yurei. Tourists from all over the globe would come to Ryokan Hiei to try and see her ghost, but the phenomena they encountered was so frightening that even the ghost hunters couldn't stand it.
In 2010, Nancy discovers a letter from Kasumi to her daughters that says neither of them have to run the ryokan if they don't want to; she wants them to be able to live the lives they want to lead. She goes on to say that she wants them to be closer together and that if she had her way, she would be with them always. To reach the letter, the girls would have to work together to solve a nonogram puzzle, and to ensure that they would, Kasumi planned to give each of them half of the numbers needed to solve it on their fifteenth birthday. Unfortunately, she died when Yumi was fifteen, meaning she never got the chance to give Miwako her half. Luckily Nancy found it and was able to show the girls their mother's note, leading the two girls to form a better relationship with one another.
- Takae felt extremely guilty over her daughter's death and firmly believed that Kasumi's ghost was haunting the ryokan to take revenge on her.
- When Kasumi was Yumi's age, they apparently shared very similar personalities.
- Kasumi described her eldest daughter as a "free spirit".