Yui Hirahara is Kousuke's mother, & wife of Randulph Hirahara. She is a businesswoman in the Hirahara Corp, in charge of the Health Facilities.

Yui is portraited as a business minded woman, in which she determines the worth of a person depends on the person's potential contribution that can benefits for her agendas, especially for her son's future as Hirahara Corporation's president.

Yui can be very blunt sometimes. In one of the latest chapters, she defended Shin-Ae from Megan's unending bickering.

Yui is also very observant and clever. She realized that her son Kousuke seemed intrigued by Shin-Ae, and managed to get the exact reaction out of him that she wanted, by hiring her as her assistant for the day. By doing that, she was also able to uncover Shin-Ae's home life