The Aeon Shiva, who appears as a Macalanian priestess, was obtained by Yuna when she visited the Fayth in the Macalania Temple. Possessing the highest initial Agility and Evasion, Shiva starts out knowing only ice magic. However, she can be taught any ability provided that her summoner has all of the items necessary.
Quite a daring cosplay to wear in the Anime Expo 2011, but I suppose that makes it all the more impressive. Thanks again to Stilzkin for sending this in!