Things didn't end up great between Krystal and Amber since they talked about their feelings that day. But since that day, Amber's feelings never faltered and continued loving her from a distance. And from a distance means being one of those f(orever nameless fans) of f(x).

Written in Krystal's POV, Number One Fan is about the young idol as she went on a visit back to the States, and discovers about Amber's secret ---- she's her number one fan.