On May 19, Iz*One shared a notice via their FanCafe, that they would be releasing their fourth extended play (EP) on June 15.
"Secret Story of the Swan" is an EDM track composed in G minor, a tempo of 103 beats per minute, and the 44 common-time signature.
As the song literally means "Fantasy Fairytale", it was written, arranged, and composed, by MosPick.
The Japanese version of the song was also written by members Nako and Sakura along with MosPick.
On the South Korean Gaon Digital Chart, the song debuted at number six, becoming the group's second top ten hit in the country.