A full-time housewife and former teacher, wife of Kang Joon-sang. Her eldest daughter is Kang Ye-seo and her second is Kang Ye-bin. After moving into the grand, European-castle-like SKY Castle when Joon-sang was promoted to full professor of orthopedic surgery at Joonam University, she became the envy of even the top 0.1% for her perfect support of her husband and education of her daughters. However, even she has a rival: Cha Ji-woo, the daughter of Cha Min-hyuk and No Seung-hye. Unlike Ji-woo, who gets perfect scores without even attending private academies, Ye-seo makes mistakes due to nerves, leading Seo-jin to constantly scold her.

The eldest daughter of Han Seo-jin and Kang Joon-sang, a first-year student at Shin-ah High School. Inheriting her father's brilliant brain and her mother's ambition, she is a top student overflowing with energy when it comes to studying. She is a person of such grit that she cannot sleep if she doesn't take first place. She is jealous of Ji-woo, who gets perfect scores without attending academies.

The second daughter of Han Seo-jin and Kang Joon-sang, an eighth-grader. While her brain is as sharp as Ye-seo's, her rebellious streak outweighs her desire for achievement. In short, she has no dreams or career goals, and her grades are only mid-tier, making her a daughter who is 98% lacking in the eyes of her mother, Han Seo-jin.

A full-time housewife who completed her doctoral coursework. Mother of Cha Se-ri, Cha Ki-joon, Cha Seo-joon, and Cha Ji-woo, and wife of Cha Min-hyuk. Raised by a father who was an Army Chief of Staff and a member of the National Assembly, she lived a life where even a towel had to be folded with perfect angles. Perhaps because of this, she has no particular competitive streak and does not want her children to live a life of walking on eggshells just to be number one. However, her husband's values, which are diametrically opposed to hers, are always overwhelming. Pushed by Min-hyuk's greed, she does her best for her two sons' entrance exams, but she is constantly compared to Han Seo-jin for being 'a step behind' and is driven to madness in silence. She is exceptionally beautiful and is the only one in SKY Castle who married for love.

No Seung-hye's husband and a professor at Joonam University Law School. Father of Cha Se-ri, Cha Seo-joon, Cha Ki-joon, and Cha Ji-woo. The embodiment of ambition. Since childhood, he has been all-in on his studies with an extraordinary competitive spirit. Having grown up in a poor family, he is always filled with longing for status. Consequently, Min-hyuk places his cherished pyramid in front of him and begins brainwashing Ki-joon, Seo-joon, and Ji-woo, saying, 'I climbed up step by step from the bottom, so if you get this far, your children's generation will be able to stand at the very top of the pyramid.' He is the only one in SKY Castle who married for love.