Question: What was the first single by the former band member and leader of "1st-generation K-Pop idols" in South Korea?
Sentence (from "Sechs Kies"): Consisting of members Eun Ji-won, Lee Jai-jin, Kim Jae-duck, Kang Sung-hoon, Ko Ji-yong and Jang Su-won, the group debuted on April 15, 1997.
Relevant evidence: No