Paine is a Sphere Hunter that is part of YRP along with Yuna and Rikku. The three are looking for clues and answers that may explain the nature of a sphere that Yuna saw. The sphere is of a young man that resembles Yuna's lost love, Tidus. So Yuna goes in search of this man who we find out is Shuyin, a spirit that is taking control of people.
When Paine was a sphere hunter with, Gibbal, Baralai, and (???), she was recorder and witnessed Shuyin's influence first hand as all three of the men lost control and attacked each other.