- “To live without one's anima is not really to live.”
Using auracite drains a person's anima little by little, leaving them more and more apathetic until they eventually stop feeling any emotions. The stolen anima can be used to create Yarhi in the World of Illusion; these Yarhi can then be summoned by others possessing auracite. Anima stolen this way are trapped in auracite crystals, particularly in the massive auraliths.
Those who have had their anima stolen seem distant, emotionless, and apathetic, which Vaan and his party note when they meet the aegyl Llyud. Llyud provides much of the game's explanation of anima as he slowly regains his while in the party. By comparing the passion Vaan and the others display in helping others to the cruelty of Ba'Gamnan's pursuit of Balthier, Llyud notes that anima can drive people to good deeds or to bad; he also speculates that Fran's uncanny ability to read people stems from her anima. His anima begins to return after the auralith's destruction, which he finds bewildering at first.
When Vaan disappears, Llyud is surprised at the sense of loss he feels; Penelo has to explain that grief is a normal feeling when losing a friend. Later, Vaan declares that it is good to feel anger and sorrow as well, because they are also part of life, but Llyud decides emotions that take on another's suffering are sometimes a cruel thing to feel.
Feolthanos began using auracite and the auraliths to steal anima from the aegyl soon after they came to Lemurés, which granted him immortality and allowed him to control the aegyl. Over these thousands of years he crystallized into a giant auralith himself, losing most of his anima and retaining only feelings of hatred and anger. The harvested anima within the auraliths find rest in the World of Illusion, and aegyl and Yarhi are both slaves to Feolthanos's will.
When the Sun-Cryst explodes, the swell of Mist breaks the barrier around the sky continent and Sky Pirates start to appear throughout Lemurés; Feolthanos uses this chance to steal their anima as well, along with the anima of one of the last members of his own family, Mydia, whom he turns into the Judge of Wings and uses to invade Ivalice.
Feolthanos tricked Mydia by promising to resurrect her dead love, Velis, when really he used her anima to create an illusion with Velis's form. The party meets this Velis in the World of Illusion, the realm of the Yarhi they are sent to after Balthier destroys the second auralith. Before he transforms into the Yarhi Odin, Velis explains the relationship between anima and Yarhi: summoning Yarhi requires the summoner to surrender a piece of their anima, and surrendered anima that is tainted with evil becomes a beast.
He tells the party that, through Mydia, Feolthanos means to gather the anima collected in the auraliths and use that power to lay siege to Ivalice. Velis begs the party to destroy him, so that Mydia might regain some of her anima, and to destroy all the auraliths and release the anima they hold before Mydia can drain that power.
When Balthier destroys the second auralith, some of the aegyl's anima returns to them. However, as Fran explains, base emotions are quickest to surface, and so many aegyl turn their new anger and hatred against Ivalice. This complicates the party's attempts to track down Mydia, as they must keep the aegyl from invading Ivalice, but they do eventually find and defeat her. Mydia regains her anima when her Judge of Wings guise is destroyed, and although it is too late to save her, her released anima guides the party to the Keep of Forgotten Time where Feolthanos lives.
There they must defeat ghostly visions of aegyl formed from the anima trapped in the Keep. When the party finally confronts Feolthanos, he claims he drains the aegyl's anima to keep them from suffering, doing them a favor by giving them a peaceful world and protecting them from sorrow, anger, and hatred. The party also learns that Feolthanos placed part of his anima in the auracite he left in the Glabados Ruins, linking it to his soul so his viera family back on Ivalice might one day find it, summon the airship Galbana, and follow him to Lemurés.
Once Feolthanos has been destroyed, the aegyl fully regain their anima and leave Ivalice to look for a new home. The Yarhi, manifestations of the stolen anima, disappear from the world, and the Galbana, brought to life by Feolthanos's original anima, flies away and disappears.