Khione is the daughter of Boreas the God of the North Wind and Winter, the sister of Zethes and Calais, the Goddess of Snow in Greek mythology and is a supporting antagonist in The Heroes of Olympus books The Lost Hero and The House of Hades.
The Heroes of Olympus
The Lost Hero
Khione first appears in December when three demigods Jason Grace (a son of Jupiter), Piper McLean (daughter of Aphrodite) and Leo Valdez (son of Hephaestus) (who are on a quest to find and free Hera before the winter solstice) come to Boreas's penthouse in Quebec where they meet Khione and her immortal demigod brothers Zethes and Calais. Leo develops a crush on Khione, but she doesn't reciprocate as she senses fire within him (as Leo can produces fire) and makes Leo wait with Calais whilst she and Zethes take Jason and Piper to Boreas. Khione supports the idea of freezing Jason (whom Khione would want for herself) and Piper, but Boreas disagrees. She is angry at her father for this, but is forced to listen and results in letting the demigods go.
Later when Jason, Piper and Leo fly over Detroit, Khione summons a strong wind that knocks the demigods metal dragon Festus out of the sky and freezes the wires in his head and causes his control disc to be damaged which results in preventing him from flying. The group don't suspect Khione of this damage.
She later tells Lycan and his wolves to track the demigods and their satyr Gleeson Hedge down. When the demigods and Hedge visit the master of the winds Aeolus, their godly parents convince him to help their children, but before he does, Khione whispers to Aeolus that Gaia is waking and that he must kill the demigods. But before this can happen, Aeolus's nymph assistant helps the group escape and get them to California.
Khione reveals herself to the demigods at the Wolf House and reveals her responsibility to the problems they faced on their quest and her alliance with Gaia's forces. She also reveals her plan to overthrow Boreas and that she convinced Zeus to close Olympus by saying that the gods being active on Earth is the cause of Gaia's awakening. Khione, knowing of Leo's feelings for her, tries to convince him to join her cause. However Leo (angered that Khione was responsible for damaging Festus) turns down her offer and uses his fire powers to knock her down, but Khione is able to escape by turning into snow and melting just before Leo tries to hit her with a flaming hammer.
The House of Hades
Seven months later in July, Khione along with Zethes and Calais ambush Jason, Piper, Leo and their fellow demigods on their ship the Argo II. Khione blasts Leo off the ship and freezes Jason and seals away Frank Zhang, Hazel Levesque and Nico di Angelo with ice. However before Khione and her brothers can take further action, Piper uses charmspeak to activate Feastus (now the figure head of the Argo II) who's fire vaporises Zethes and Calais. Khione tries to freeze Piper, but Piper fights back and stabs the snow goddesses with her knife Katoropis, causing Khione to disappear in a flurry of snow.