Anima is an optional Aeon in the game, which involves you doing a lot of things in order to get her. To start, you have to collect all of the Destruction Sphere treasures in the temples, two of which you will want to do on your main story visits, due to Dark Aeons blocking the entrances later. Once you have done all of that, continue in the main story until you gain full control of the airship. Uncover Baaj Temple and defeat the boss there, than enter the temple. Interact with the statues on the sides, which will light up if you have collected the Destruction Sphere treasures. Once all six are lit up, the way to the Chamber of the Fayth will be open, where you will get Anima.