Chairman of FT Group and father of three children. Living amidst the sorrow of losing his wife and a heavy sense of responsibility, he finds his heart constantly wavering for Park Dan-dan, the live-in tutor who entered his home. Usually a strict and serious gentleman, he possesses an unexpected boyish charm, getting jealous or sulky in front of Dan-dan. Due to the difference in age and social status, he is currently in 'denial of his feelings,' trying hard to suppress his heart.

Born into a poor family, she possesses a resilient personality that never yields to any trial. She enters Chairman Lee Young-guk's house as a live-in tutor, healing the children's wounds and becoming the center of the family. She is cheerful and bold. After realizing her feelings for Chairman Lee, she is a lover who charges forward fiercely, undaunted by the difference in status or the gaze of those around her.

The manager in charge of the household affairs at Chairman Lee Young-guk's residence. She has long aimed for the position of Young-guk's wife, but when her plans begin to crumble with the appearance of Park Dan-dan, she starts to spiral. She is cunning and calculating. Since she doesn't have the 'amnesia' cheat code, she engages in elaborate psychological warfare, creating misunderstandings between Young-guk and Dan-dan and subtly using the children to try and drive Dan-dan out.

Lee Young-guk's eldest daughter. A teenage girl who closed her heart and wandered due to her mother's absence and her father's indifference. On the outside, she is prickly and grumbling, but on the inside, she is deep and warm. At first, she was wary of Dan-dan, but after feeling her sincerity, she becomes Dan-dan's reliable ally and romantic supporter.

Lee Young-guk's second son and a troublemaking prankster. He is like a vitamin that brings laughter to the house. He is quick-witted and clever. He is the first to notice that his dad and Teacher Park like each other, and he is a cute cupid who devises all sorts of operations with his younger brother Se-jong to bring the two together.

Young-guk's youngest son. He suffered from separation anxiety due to his mother's absence but finds stability after meeting Dan-dan. He is full of aegyo and innocent. He follows Dan-dan like a mother, saying, "I want to live with Teacher Park forever," and he is a 'gum-sticker' who listens to whatever Dan-dan says.