Hanabishi Kaoru's mother.

The Hanabishi family didn't like or approve of her, as she was considered by them to be a woman of low station, so she was never "officially" married to her husband, Hanabishi Yuuji. When Yuuji died in a sudden car accident, and having no other heirs (that they knew of), Kaoru was acknowledged as the "official" heir of the Hanabishi family, but on the condition that Kumi leave the estate and never have contact with Kaoru again.

Kumi passes away when Kaoru is in high school, though it is never stated how she dies. Her death was the breaking point for Kaoru to leave the Hanabishi, as he only stayed to fulfill her wish that he have a prosperous life.