Sim Gyu-seon (심규선), formerly known as Lucia (루시아) is a South Korean indie pop singer-songwriter under GYU (헤아릴 규). She used to be signed to Pastel Music (파스텔뮤직) from her debut in 2010 to the end of 2016. Since her departure from the label, she goes by her real name. She debuted in 2010 with the song "고양이 왈츠" (Cat Waltz) in the single "첫번째, 방" (The First Room).