This woman was the mother of Kazuo Kiriyama. As soon as he was born, Kazuo could remember his mother was always happy. She would always be impressed with how her child would cope with things as he was very cheerful and helpful, while being smart.
One night would change everything. She, Kazuo, and their driver were hit by a sleeping truck driver. She would lose her life, while her son would lose his emotions as a result of the accident.
Interesting fact - Brain injury which cause losing emotions does not exist, and combinated with geniality is not naturaly possible, which makes the theory of Kazuo's personality impossible. There are autists (like in movie Rainman, that are genial in some sort of activities (and only in one or few) but are unable to live on their own because they have no motivation to do something)