Xion (played by Sammi) is Rank XIV within Organization XIII.
In Demyx Time 11, Xion appears to be very childlike, having tea parties with plush dolls. She is revealed to be something of a conspirator, as the secret lover of the evil Fridge Goblin, and loans Demyx money.
In Demyx Time 12, she plays the part of a transfer student who befriends the Losers, and becomes the rival of Larxene, who wants to be the only girl in school again. Roxas and Xion seem to have a moment, but later it is revealed he's really in a relationship with Axel. She is still fairly childish, as shown when she spells "difficulty" with a nursery rhyme (referencing "Matilda" by Roald Dahl).
She plays the part of the maid in Demyx Time 13, where her potential motive for the murder of Vexen is her association with the Fridge Goblin. She is shown as fairly inteligent, but dismissed by others as a "silly cow". She is murdered by Larxene before the end of the episode.
She is only briefly seen in Demyx Time 14, in the alternate present seen by Luxord where she is noted to have lost a lot of weight, a completely different personality, and appears to be in a relationship with Roxas.
Xion's Organization coat is similar to the one Roxas wears, with slightly pointed shoulders and closer-fitting sleeves. She also wears the more feminine, heeled boots that Larxene wears and the basic black gloves. Physically, Xion strongly resembles Kairi in her appearance from Kingdom Hearts, having her blue eyes and virtually the same hairstyle, though Xion's hair is black and her bangs part on a different side. She is slightly shorter than Roxas.