Princess Lira is the formidable siren princess of the Diávolos Sea, known ominously as the Princes' Bane. She specifically hunts royal heirs and collects their hearts to please her brutal mother. Following a severe breach of protocol, she suffers a painful curse that transforms her into a human girl and completely strips her of her deadly siren song. Thrust into the unfamiliar human world, she schemes to track down a notorious siren-hunting pirate prince to reclaim her status and her ocean home.

Prince Elian is the crown prince of Midas, the golden kingdom, but he actively prefers the dangerous freedom of the ocean over his royal duties on land. He operates as the captain of the Saad, commanding a highly loyal pirate crew dedicated to hunting down sirens. Armed with specialized weaponry, he views his violent campaign against the sea creatures as a necessary war to ensure human survival. His royal bloodline carries legends of golden blood, though he privately hides that he bleeds red just like his crew.

The Sea Queen rules the ocean with absolute authority and cruelty. Having lost her original name to her title generations ago, she suppresses any sign of compassion or emotion in her siren subjects, viewing such traits as human weaknesses. She maintains her power through terror, routinely brutalizing her own family to enforce compliance and preserve her endless war against humanity.

Kye operates as Elian's closest confidant, bodyguard, and a core member of the Saad crew. Raised as the son of a diplomat before his family formally disinherited him, he now dedicates his life to sailing and fighting alongside the prince. He maintains a deep suspicion of outsiders and directs specific distrust toward the strange human girl they pull from the ocean.

Madrid serves as the second mate on the Saad and stands as the only named female member of Elian's core crew. Originating from Kléftes, where she survived enslavement on a pirate ship from a young age, she utilizes a crossbow rather than a sword in combat. She wears traditional tattoos reflecting her culture and proves to be one of the few humans who displays immediate kindness to Lira.

Torik operates as the first mate of the Saad and is the oldest member of Elian's inner circle. Hailing from the mining nation of Ánthrakas, he possesses considerable skill with both a sword and a pistol. He holds the distinction of being the very first person to join Elian's crew when the prince initially took to the sea.

Khalia is a young blonde siren with one milky eye who possesses a rare, close bond with her older cousin Lira. She frequently faces the Sea Queen's wrath, bearing harsh physical punishments for Lira's infractions. Despite her brutal environment, she maintains loyalty to her family while navigating the deadly politics of the ocean.

Princess Yukiko is the younger sister of King Kazue and the princess of the icy northern kingdom of Págos. She possesses highly valuable information regarding the geography of Cloud Mountain and the artifacts hidden there. She approaches royal politics strategically, using her geographical knowledge and royal bloodline as leverage to secure advantageous political alliances for herself.

Tallis operates as the ruthless captain of the pirate ship Xaprár. He commands a crew of thieves from Kléftes and holds a broad reputation for stealing artifacts from human royalty. He actively pursues leverage and wealth, making him a highly dangerous adversary on the water.

Crestell is the Sea Queen's sister and Khalia's mother. She holds a tragic place in Lira's past, having made a critical sacrifice to protect her young daughter from the Sea Queen's cruel and impossible demands.

Galina rules the kingdom of Eidýllio, a land heavily associated with romance and sweet scents. She bears a magical family curse where any man who touches her becomes obsessively devoted to the point of complete insanity. Consequently, she remains unmarried and heirless, leaving her kingdom politically vulnerable to rival nations.

Amara is the young princess of the golden kingdom of Midas and Elian's sister. Unlike her brother, who wishes to completely escape royal obligations for the open sea, she possesses a strong ambition to lead and actively desires to take the throne for herself.

Radames serves as the king of Midas. He worries constantly about his son's dangerous lifestyle hunting sirens and continuously presses Elian to abandon the sea to properly prepare for his future duties as the kingdom's ruler.

The Flesh-Eater is a monstrous, nameless merman from the depths of the ocean. Following strict siren mating traditions, he claims ownership over Lira, possessing a decaying, grotesque physical form that repulses even her.

Kazue is the ruler of Págos, recognizable instantly by his ceremonial snow lion headdress. He oversees access to the sacred Cloud Mountain and demands significant concessions and artifacts from anyone seeking permission to climb it.