For the Kim Kwang Suk special of the show, VOISPER covered his 1993 song "Letter of a Soldier". The four talented vocalists were the last performers of the episode, and the members expressed, "It was the song we related to most," referring to their own mandatory military enlistment.
[ SPOILERS BELOW ]
VOISPER's touching performance won them the round against That Summer's Zoo musical team, which included Yoon Hee Suk, Choi Seung Yeol, Lim Jin Woong, and Hong Kyung Min, giving them their first 'Immortal Song' win. The vocalist group took the final win with 430 points.
Congrats to VOISPER!