US - North Korea Relations: Why Is Kim Jong Un's Sister Speaking Out Instead Of The Supreme Leader? 03/17/21 AT 5:37 PM Kim Jong Un’s sister Kim Yo Jong has attained new heights of prominence, recently delivering a stark warning against U.S. action in Asia. She’s played an increasingly important role in North Korean governance, especially when it comes to relations with Washington. “If [the U.S.] wants to sleep in peace for the coming four years, it had better refrain from causing a stink at its first step," she told state news. Kim Yo Jong is a trusted adviser to her brother and was a key voice when inter-Korean tensions mounted last year Photo: POOL / JORGE SILVA