|Professor Kim Jin-woo|
|Cast in Drama||Jung Dong Hwan|
|Anime Vocal||Bae Han Seon|
Prof. Kim Jin-woo, as the name suggests, is a mathematics professor. He is the most trusted friend and confidant of Jung Hyunsoo. He used to conduct private math classes for Joonsang. He is the person who sheds light on the question of Joonsang's true father. He is Joonsang's father. He is married to Kim Jung.
He possess a kind and intellectual face ,thereby he is well-respected among other individuals as a professor in a university. Being a University Professor, he often wears a semi-formal suit for his classroom discussions. He wears glasses and usually dresses up in formal suits for most occasions.
He is a calm and reserved person, who takes his teaching profession seriously. Providing additional support and help to interested students like Joonsang.
He can also be very persistent about certain things like the question of Joonsang's true father.
Kang Joon-Sang/Lee Min-HyeongEdit
He is married to Kim Jung and has a son with her. At first part of the anime series, they make a well-going couple but when he discovered that he had a son name Joonsang from Kang Mee-hi, it made her to be ill and show apathy toward his husband.
He is more than a just father to Sanghyeok, acting as a friend and helping through all his emotional turmoil.
She is close family friend of Kim Jinwoo. They were always on good terms with each other thanks to his friendship with Jung Hyunsoo.
Prof.Kim is like a father to Yoojin and is always by her side.
At the start of the anime series, he always appeared in a classroom or faculty lounge interacting with students. He was often seen discussing things with Joonsang regarding mathematics. But Joonsang would often ask him about Kang Mee-hi ,and things which would throw light on his fathers's identity.
He was always doubtful as to who Joonsang's father was. Never completely convinced of Kang Mee-hi's word, he asks a doctor to do a DNA profiling on Joonsang in the sequel. The test proves that he is Joonsang's father and not Jung Hyunsoo.
- He is an excellent Mathematics teacher.
- He is able to recognize the best student Joonsang even after a gap of ten years.