Il-hoo, who is back to school after his military discharge, meets Chae-heon through mutual friends. It seems difficult to understand Chae-heon, who is always smiling; sometimes, he approaches Il-hoo with sweet words and a pretty smile, while at some other moments he does it suspiciously like an argument. "I don't know the real him." The "exploratory battle" between the two of them, starts now.