The ocean is an important place for both Lira and Elian. Lira is a sea creature and has lived her entire life in the ocean. For Elian, the ocean represents freedom, and he sails on the Saad to escape his royal life. In fiction, the ocean commonly symbolizes many contradictory ideas. It is comprised of water, which gives life as easily as it takes life away. The ocean is also incredibly vast, covering most of the surface of the Earth. It’s as beautiful as it is daunting, and it is full of mystery; the idea that the ocean is full of horrors and unknowns is as old as folklore itself. Christo presents a dangerous version of the ocean, full of sirens who hunt for human hearts. At the same time, she presents the ocean as a place of beauty and wonders. The Diávolos Sea, the home of the sirens, is impossibly blue and clear, both beautiful and magical.

Hearts appear as a symbol throughout the book, both literally and metaphorically. While the sirens actually steal physical hearts, the act also becomes a metaphor for falling in love. Lira tells Elian that stealing a siren’s heart gives a human immunity to siren songs.