Some songs in the game have had alternate versions added to the game for special occasions. These alternate versions are available for only a short amount of time (typically five days including the remaining portion of the first day they become available, unless otherwise stated).
One type of these are the birthday solo songs, which are released on any given member's birthday.
Others have also been added at various points: (note that this list is out of date)
|Lovely Summer||Mei, Suzune||September 3, 2016||Event winners|
|Lovely Summer||Hinata, Hotaru||September 3, 2016||Highest avg. points in event|
|Sentehisshou Smile||Akari, Yukina||September 27, 2016||Determined in corner at 1st live|
|Shiny||Hinata, Suzune||September 27, 2016||Determined in corner at 1st live|
|Halloween☆Night||Hinata, Akari, Ayame, Mei||November 7, 2016||Event winners|
|Happy♡Merry||Mei, Hinata||December 25, 2016||Event winners|
|DREAMER||Hinata, Akari||March 31, 2017||Event winners|
|Fantasia April Fools' ver.||All||April 1, 2017||Available for one day. Was only a new note chart for the normal tutorial-length version.|
|Rooting for You||Akari, Ayame, Hotaru||September 1, 2017||Event winners|
The coin songs from the premium shop are also alternate versions of existing songs, but they do not have fixed time windows in which they can be played.