Sirene's Dress

 Sirene's Dress is a sub-location located on the other side of the island where Sirene is located. Sirene's Dress is a location associated with Lune's relationship side quest, which involves Lune's character story, where she asks Verso to help her understand and learn about her parents' expedition. This dialogue is only available when you speak to Lune in Camp and before you increase the relationship level to Level 6.