She was born in Gwangju but moved to California when she was 3 because her mom had the opportunity to teach at Cal-Berkeley. She is the youngest of five kids and lived with both parents but is a daddy's girl. She went to one of the top STEM schools in Berkeley, where she learned English and how much she really loved music. However, after receiving a better job and salary at SNU, they went back to South Korea, when she was 7. Given her new love of music and wanting to perform, she auditioned for SM Entertainment. 

 

Currently, she is appearing on Mnet's girl group survival show, MUSE, and was announced as the first official member of the final group. Shortly after, Kassy had signed a dual contract with Galaxy Entertainment and SM Entertainment.