"Rikku is a 15 year-old Al Bhed who helps Tidus when he first arrives in Spira, but then disappears from the story for a while, becoming the last character to join Yuna's entourage of guardians. She is bilingual, able to speak both English and Al Bhed fluently. Rikku's character class is most similar to that of the Thief from earlier Final Fantasy titles, combined with the Chemist class. She can steal a large variety of items from fiends and bosses alike, many of which can only be acquired through theft. She also is able to dismantle Machina with her theft command. The ability to customize becomes unlocked only after Rikku permanently joins the party. Her attitude is somewhat childish, but is also quite cheerful and positive. An Al Bhed, she is also Yuna's cousin and loves her dearly, and, as such, wishes to prevent her from going through with her pilgrimage, becoming particularly insistent as the party climbs Mount Gagazet toward Zanarkand. She is also the one who informs Tidus that Yuna would die if she summoned her Final Aeon. In battle, Rikku uses a variety of claw-like weapons. After the Calm, Rikku visited Yuna at Besaid often before the events of X-2. Rikku returns in Final Fantasy X-2 as a main protagonist, now seventeen years old and prominently featured as a Thief. She was also the one who convinced Yuna to leave Besaid on a journey after showing her a mysterious sphere featuring a familiar person.
Rikku also appears in Kingdom Hearts II as a miniature fairy version of herself wearing modified versions of her Final Fantasy X-2 attire. Much like her Final Fantasy X-2 self, Rikku is a bit ditzy and good-natured as well as a treasure fanatic like her teammates. Itadaki Street Special features a miniature Rikku in her Final Fantasy X-2 outfit, along with Yuna and Paine."
Source: Wikipedia, "Rikku", available under the CC-BY-SA License.