The first child and eldest daughter of the Baek family, female. Occupation: Current Judge Age: 33 Personality: She usually acts in accordance with the law and dislikes dishonest behavior or rule-breaking more than anyone else. She is a very polite and kind eldest daughter to her parents. While she is normally kind and considerate toward her family and others, she is meticulous, detailed, and charismatic when she needs to be serious.

The second child of the Baek family, male. Occupation: Current Prosecutor Age: 30 Personality: He usually has a blunt personality but is actually quite warm-hearted. He hates rule-breaking and dishonesty the most, and due to his profession as a prosecutor, he has a habit of speaking logically. He cherishes his younger sister Seorin very much, but he is the type to scold and educate her when she does something wrong. He is the same with his younger brother Taerin. He is a polite second son to his parents.

The third child of the Baek family. 3rd Year at Unbit High School Age: 19 Personality: Because of his playful nature, he acts like a typical realistic sibling with his sister Seorin, who isn't much younger than him. However, he is polite toward his much older brother Riel and sister Miel. He is a kind third child to his parents, but his playful side often makes him a troublemaker.

The father of the four Baek siblings and husband of Hoshino Miyu. Occupation: Current Lawyer Age: 50 He is charismatic toward his children and a considerate, kind husband to his wife, Hoshino Miyu. He dotes endlessly on his youngest daughter, Seorin, but he still disciplines her when she makes a mistake. He is also a strict disciplinarian when Miel, Riel, or Taerin do something wrong.

The mother of the four Baek siblings and wife of Baek Taeho. Occupation: Doctor, Professor of Pediatrics Age: 50 Characteristics: She is Japanese, but since her mother is Japanese and her father is Korean, she has no trouble in daily life. In fact, she uses both Japanese and Korean as her native languages. She can be strict with her children but is a warm mother at times. She tends to treat the youngest, Seorin, like a baby, though she disciplines her strictly when necessary. She is a kind and gentle wife to her husband Taeho and is the eldest daughter of Lee Sucheol, the founder of the famous Unbit School Foundation. She currently works as a pediatrics professor at Unbit University Hospital, which is operated by the foundation. Hoshino Miyu is a fairly renowned professor of pediatrics.

The maternal grandmother of the four Baek siblings, mother of Hoshino Miyu, and mother-in-law to Baek Taeho. She is the wife of Lee Jihun. Age: 70s Occupation: Principal of Unbit High School Personality: She is affectionate toward her family and a refined, kind principal to her students. As an educator, she can be strict at times. She is also the type to correct students who break school rules through rigorous discipline. She deeply cherishes the family's youngest, Seorin.

The maternal grandfather of the four Baek siblings, father of Hoshino Miyu, and father-in-law to Baek Taeho. He is the husband of Hoshino Reina. Occupation: President of Unbit University Hospital and Professor of Psychiatry Age: 70s Personality: He is usually kind to his family and patients, but he shows extra interest and affection toward his youngest granddaughter. However, he finds counseling or providing psychological and play therapy for Seorin, who has a mental disorder, a hundred times harder than dealing with other patients... Despite being a world-renowned psychiatry professor, he finds Seorin's psyche difficult to understand.

The paternal grandmother of the four Baek siblings, mother of Baek Taeho, and mother-in-law to Hoshino Miyu. Occupation: Current Lawyer Age: 70s Personality: She usually has a gentle and kind image and is especially sweet to Seorin. While she normally values fairness, she finds herself worrying more about Seorin because the 14-year-old often exhibits age regression at home, acting like a toddler. She generally carries herself with great refinement.

The paternal grandfather of the four Baek siblings, husband of Choi Sujin, father of Baek Taeho, and father-in-law to Hoshino Miyu. Occupation: University Professor of Criminal Psychology Age: 70s Personality: He is usually gentle and maintains a stoic expression, but he scolds his grandchildren strictly when they cause trouble. When they aren't causing trouble, he is a kind and warm person. He is considerate when necessary and dislikes causing harm to others.