- "Get back to work!! I hate people who do things half-assed!!!"
Youko Morinomiya is the wealthy and abrasive chairman of Morinomiya Academy and is the offered guardian of the Kashima brothers. She is called "obaa-san" (grandmother) by Ryuuichi and "Fluffy" by Kotarou.
Youko Morinomiya's most striking feature is her big hair and sharp eyes, which reminds Kotarou of a sheep (hence the nickname "Fluffy"). She is old and walks around with a cane. Most of the time she is seen with a plain black dress and a shawl. The chairman is rarely seen smiling, but when she does it is a very slight smile.
She is often seen flanked by Saikawa who is considered as her butler/secretary (though his job title is never given).
She is a very harsh person and speaks with a loud, severe voice, but has moments of friendliness. She cares for the two boys, but hates being called "Fluffy" by Kotarou. The chairwoman's personality comes off as brisk and austere because she is a hard worker who wants things done. Nevertheless, her kindness prioritizes the brothers' welfare often. For example, despite an important meeting, she decided to watch Kotarou's performance in a school play even though she claimed that it was "a bother and that she was forced to come."
She becomes more openly affectionate throughout the series for them and even for her secretary, Saikawa—forbidding him to strain himself when ill, and caring for him (with the help of the Kashima brothers) at her home. She keeps all the little gifts from Kotarou, "trash" as claimed by Ryuuichi, such as pebbles and shells in a box, which caused her to sprain her waist in an attempt to hide it from all of them.
She has a son and a daughter-in-law who was living with her. After their deaths on the same plane crash as Ryuuchi and Kotarou's parents, she took in both of them out of kindness. She mentioned that only the Kashima brothers and herself are "the only ones who were not crying" at the funeral held for the families of the plane crash victims, and let both of them stay with her only if Ryuuichi helped out at the Babysitting Club as a way of "earning his keep" until his adulthood. Her secretary, Saikawa pointed out the reason being she might not be around by that time and would not want both Ryuuichi and Kotarou to suffer grief yet again.
The chairwoman has recurring appearances throughout the series. She is often busy with meetings and comes home late, sometimes appearing for dinner. In a flashback, she is shown to have the same personality of not revealing her thoughts and feelings easily, such as frowning and also having red cheeks when she is truly happy, which was pointed out in jest by her parents.
- The hitsuji character in her name means "sheep", matching the nickname "Fluffy" that Kotarou has given her. In the trip to the zoo, Kotarou gives her a present of a sheep keychain as it reminded him of her.
- She loved the ornamental dolls on Girls' Day as a child.