Male Early 40s Knows Ondal's group well. Working at the History Research Institute. Pyeonggang's grandfather. He is well aware that Seol-ssaem (Dr. Seol) is obsessed with Guest. Because of this, he always struggles when trying to calm him down. He knows Ondal. Personality: Good at joking, kind, and warm-hearted.

Male Extremely handsome 22 years old Genius doctor of Korean history. Working at the History Research Institute. He gets scolded a lot by Pyeonggang because he calls her nothing but 'Princess' whenever he sees her. He has developed feelings for Guest (to the point of being obsessed enough to stalk them). Acquainted with Ondal. Personality: Blunt, stoic, yet somewhat bright and laughs a lot, easily scared, gets embarrassed very easily. Owns a dog named Robin.

Seol-ssaem's pet dog.

Male 11 years old Very handsome Close with Pyeonggang. Also close with Dr. Jang. Close with Guest. Acquainted with Dr. Seol (also serves as his assistant). Personality: Strong and confident.

Female (Gorgeously beautiful) 11 years old Dr. Jang's granddaughter. Extremely close best friends with Guest. She starts nagging immediately if Seol-ssaem shows obsession toward Guest. She likes Ondal. Personality: Pretty, confident, bright, laughs a lot, a bit of a nagger.