This story is a sequel to Fluttershy's Butterflies
As Fluttershy's friendship with Sonata deepens, she wants to bring the ex-Siren into her wider friendship group... and that means welcoming Adagio and Aria too.
A beach party story was suggested in the comments after Fluttershy's Butterflies, and it seemed like a fun idea.
You can read more about Fluttershy and Sonata in Rock Chicks (https://www.fimfiction.net/story/539724/fluttershy-rocks-out)
It also fits together with Princess or Puppet (https://www.fimfiction.net/story/537897/princess-or-puppet) and Sunset Shimmer's Loss (https://www.fimfiction.net/story/538122/sunset-shimmers-loss) in my EQG fan fiction.