Download Song Seung Hyun (FTISLAND) - 우리사이 (What's the definition of us) MP3 from album "Oh! My assistant OST Part.1". All MP3/songs are for personal, non-commercial use only. Please support Song Seung Hyun (FTISLAND) by buying their original song, Available on iTunes, Spotify, JOOX, Amazon, or other Official Music Store. Best regard.