Why is Noriko Katsura an important character in the novel, Inheritance From Mother?

Noriko Katsura is Mitsuki and Natsuki’s mother. Noriko is central to the story because it is about her death and the relationship she had with her daughters that is central to the story. Even though Noriko treated Mitsuki unfairly when Mitsuki was a child, Noriko puts on Mitsuki the burden of caring for her physically and emotionally when she becomes sick.