The title song '5K' of this album contains Lee Jin-hyuk of Twinty Six who matured both inside and outside.
About Lee Jin-hyuk
Lee Jin-hyuk, formerly known by the stage name Wei, is a South Korean singer, rapper and actor. He debuted as a member of South Korean boy band UP10TION in 2015. In 2019, he rose to fame after finishing 11th on Produce X 101.
 Wikipedia