Lee So-Yeon is the late mother of So-Yoon, and the first person to reject becoming a Medium.
Lee So-Yeon was born with spiritual powers, and as a result, a ninetails came out of the Scroll to protect her. While it was considered honourable to become a Medium, Lee So-Yeon thought otherwise, and felt sorry for Banya, wishing for him to have time to find who he needs to find in order to be free of the Scroll, finding his imprisonment to be too cruel.
One day, So-Yeon decided to leave home to marry a man she liked. A year later, however, her husband passed away in an accident, and Banya is said to have been visiting her everyday since, probably out of worry. Although Banya informed her that it was alright for her to receive a God, So-Yeon decided to put off doing so to allow him to find the reincarnation, feeling worried that he's forgetting his task becausing he's trying to protect her.
At this point, So-Yeon is pregnant, and has passed such information to Ajussi. Shortly after, So-Yeon returns home but is harshly yelled off by her mother. Instead, So-Yeon secretly goes up the dangerous moutain, not telling Banya, and ends up dead, with her newborn daughter in her arms.
So-Yeon's spirit returns to her house as one of the many ghosts her daughter can see. She informs her daughter the truth to many of her own mother's lies, such as how she herself doesn't want her daughter to become a Medium, and how she never saw the family chicken, Koko, as food. While doing so, she requested not to have her mother informed of her presence, and although So-Yoon does eventually slip this information out, it is believed that her grandmother already knew.
During So-Yoon's teenage years, So-Yeon's spirit hasn't been shown doing much but sitting just outside the house with a sad expression, and at least once, seen slipping inside the building. Ajussi has been shown to talk to her occasionally. So-Yoon notes that they haven't spoken to each other in a long time, and that her mother enjoys entering her grandmother's room.