Materia is a non-playable character in Dissidia Final Fantasy Opera Omnia.
Materia is the goddess born of Cosmos' will. She believes that the best way to protect the world is by summoning righteous individuals who will form bonds and work together, putting her at odds with Spiritus. She tends to act through a lens of logic and reason rather than emotion. However, her inability to comprehend the feelings of her warriors leads her to mistakenly take actions that drive them away from her.
Under orders from the Crystal, Materia and Spiritus create a world of respite for their warriors after their bodies and spirits risk breaking under the cycles of battle. Materia heals the warriors' bodies and attempts to heal their spirits as well by removing especially painful memories from a number of her warriors. In a small number of cases she does this with the assent of the person in question; however, for most she edits their memories without permission. In at least one instance, she chooses to remove happy memories instead (taking Yuna back to the time of her Pilgrimage rather than her self-directed life as a Gullwing) to make them more effective warriors.
The world is soon torn by its own strife thanks to the appearance of Torsions that connect to other worlds and allow monsters to invade the landscape. Materia accepts the assistance of Mog, an ancient moogle, and instructs him to guide her warriors around the landscape to repair the damage.
Materia continues to summon warriors, even those who were not involved in the cycles of battle, to increase her ranks against whatever force is distorting the world. She occasionally brings newly-summoned warriors to her throne for personal instructions; other times, she simply opens the path into the world and they either fall through or willingly enter. She makes several appearances before the group at large as they explore the landscape. However, her imperious manner and vexation at being questioned sours their relationship. Unsatisfied with either her intentions or her abilities, a number of her champions ignore her instructions and form the Returners to find their own answers. Many in the party under Mog turn towards them.
After the revelation that Mog has been deceiving them, Materia appears before her warriors in the Abandoned Petalum to explain that Mog had played both her and Spiritus' allegiences to gain power. When Spiritus arrives to give his own side of the story and assert his claim as god of the world, he and Materia quickly fall into argument before he departs. Materia orders them to enter the Dimensions' Labyrinth.
By the time she summons Ignis, the loss of her warriors' faith has resulted in Materia being visibly weakened. Uncertain of how to proceed, she allows Ignis to choose his own appearance in the timeline and sends him to find his friends. A short time later, Sephiroth enters her chambers to declare that he will take her place as a god. Materia accepts this as the will of the summoned warriors and does not resist when he strikes her down.
Despite their anger, however, there is enough faith remaining in her chosen warriors that Materia's spirit remains. Spiritus revives her and deposits her in front of the group, instructing them to restore her while he searches out the source of the corruption in the world. Her warriors, more begrudgingly in some cases than in others, decide to work together with her to maintain her position. Materia offers her apologies for creating a false respite through her alteration of their memories. When directly questioned, however, she admits that she still doesn't understand their feelings, only that she must accept them.