Park Se Yoon(Hangul:박 세 윤), or as most commonly known as Crucial Star (Hangul:크루셜 스타) is a South Korean rapper, composer, lyricist and a producer. At the age of 17, he performed with Libra Twins, a band popular in the Korean hip hop industry, and he later moved on to try an open-audition and won, landing himself with a deal with a Korean hip hop label, Soul Company. At the beginning of 2012, he released a free digital single, which highlights the aftermath of disbandment of Soul Company.