|“||I am sorry I won't be able to see you die.||”|
Unlike her siblings Triton and Rhode, Kymopoleia was never invited to see her parents, as her father Poseidon found her presence disruptive. As a result, she wanders his abandoned domains alone. She was reluctantly married off to the Hekatonkheire Briares as a reward for him supporting the gods in the Titanomachy against Kronos. She has stated that she hates her husband and that his return after The Battle of the Labyrinth brings her displeasure.
On their way to Delos, the Argo II is attacked by a sudden, violent storm. Percy Jackson dives into the water, followed by Jason Grace, who protects himself with a vacuum of air via venti (Dylan). They follow a green light to an old ruined domain of Poseidon, where Kymopoleia is using her powers to try and sink the ship, and lure Percy to Polybotes, who lies waiting.
While Percy is slowly suffocated by Polybotes' poison, Jason convinces Kymopoleia to help them, by promising to build both a Roman and Greek shrine, a custom banner, her own cabin at Camp Half-Blood, and an action figure. The idea of being feared and respected is enough to motivate her to slice off Polybotes' head.
Before Jason and Percy leave, she warns them that Percy's fatal flaw may cost them the world. She also confirms that Jason's plan to defeat Gaea could succeed. She also conveys Dylan's wish to be released upon returning to the surface, which a disgusted Jason agrees to.
Kym is mentioned by Percy Jackson when he mentions how Jason Grace convinced her to save him with action figures and banners. Annabeth Chase also mentions that she never heard the details of that, which causes Percy to blush.
Overall, Kymopoleia is driven by her desire to be feared. She states that her father Poseidon is constantly restricting her powers, much to her chagrin. Her heart has grown bitter after being cast out by her family and given over to Briares like an object. After Jason promises that she will gain recognition, she softens up a bit and even tells Jason that she finds him funny. Jason also promises:
- her first Roman shrine
- a cabin at Camp Half-Blood
- a banner
- a Kymopoleia action figure
In The Blood of Olympus, Kymopoleia was described as a 20-foot-tall goddess, wearing a flowing green dress that was cinched at the waist with a belt of abalone shells. Her skin was as white and luminous as algae fields, and her hair swayed and glowed like jellyfish tendrils. Jason also observed that her face was beautiful but unearthly, with too-bright eyes and too-delicate features, and her too-cold smile implied that she had not perfected the art of smiling. She also had a melodic voice, the resonance of which seemed to extend past the range of human hearing. As well as that, she laughs like a dolphin.
- Great Strength: Kymopoleia has great strength, even for a goddess, as shown when she decapitated the giant Polybotes (one of the most powerful of the Giants) by simply hurling a bronze disk.
- Immense Durability: Kymopoleia barely flinched when smacked in the ribcage by Polybotes' Trident.
- Hydrokinesis: As an immortal daughter of Poseidon and Amphitrite, Kymopoleia has divine authority over water and can manipulate it, to a far greater degree than her demigod siblings - such as Percy Jackson - but to a lesser degree than her father.
- Atmokinesis: As the Goddess of Violent Storms, Kymopoleia could conjure storms over the seas, such as hurricanes and typhoons. In The Blood of Olympus, she mentions that the violent storm that was sinking the Argo II was a "small taste" of what she could do.
- Aerokinesis (limited): As a byproduct of generating sea storms, she can manipulate the air above such a storm. In The Blood of Olympus, the wind roared so loudly that the Seven could barely hear each other.
- Toxikinesis: After killing Polybotes, Kymopoleia dissipated the poison killing Percy with a mere gesture.
- Kymopoleia is the only female and immortal goddess to call Percy Jackson her brother and the second sibling to call him by his full name, Perseus Jackson, along with Triton.
- Like her brother they were both introduced in the last book of their respective series Triton (Percy Jackson Series) and Kymopoleia (The Heroes of Olympus Series).
- Jason promises that she will be the first minor god he takes care of when he starts enforcing their worship.
- Interestingly, Kymopoleia is the only character in either series that is compared to a superhero from Marvel Comics (Captain America). Jason and Percy, on the other hand, are compared to superheroes from DC Comics (Superman and Aquaman respectively).
- Kymopoleia has never been honored, yet she is still powerful enough to sink the Argo II.
- She is Jason Grace's cousin.