On March 9, 2020,
Pledis Entertainment founder and chief executive officer Han Sung-soo announced he would step down from co-managing Iz*One after their first studio album,
Bloom*Iz. On March 10, a day later, it was reported that
Swing Entertainment would take part in managing the group. A source from the agency confirmed the reports and that Swing would co-manage the group. On May 19, Iz*One shared a notice via their FanCafe, that they would be releasing their fourth extended play (EP) on June 15. It announced the members were in the last stage of production and are releasing a higher quality performance. On June 1, Iz*One released an album trailer announcing the name for their album:
Oneiric Diary. On June 8, the track list for the album was released, revealing the title track to be "Secret Story of the Swan", along with seven other tracks, one being written by
Hitomi, with
Nako and
Sakura writing the Japanese version of the song. On June 11, the teaser for the music video was released, with a second being released a day later. The music video ended up being delayed a day later, set to be released the same day as the album, but was released on June 16. == Composition ==