spoilerShe acts as a kind of restraint for Ichise while he learned how to use his Texhnolyze better. While learning, he was prone to fits of insane rage, but she seemed to calm him down. After she's done with him, she follows Tatsuya around until he kills Yoshii, at which point she begins to hate her ability to see into the future because "nothing ever changes". (This, however, is a lie: In the first episode, she sees a vision of the Elder being assassinated, but Yoshii ends up saving him. Of course, it could be explained away that her powers grow the more that they occur.)
She is supposed to become the Prophet in Gabe, but the Elder explains that she can't accept her role. She doesn't want to believe in her fate or the fate of her people because it's too big a burder for her to shoulder. She hates seeing a future that is only filled with despair. Ichise desperately wanted to know his future and after much prodding, she finally tells him that he will destroy everyone and will be all alone in the end.
She eventually leaves Gabe and heads to the city, talking to her 'other self' on the way. There are kind of two sides to her: one when she wears her mask and one when she has her mask off. She heads over to the bridge in front of the Obelisk and the people of Lux begin to flock towards her and this is where we're left off.
As it turns out, she is Kanno's supposed 'Sister', Theoria. He tells us that she was the one who 'birthed' Lux. She also has the ability to talk to people through Texhnolyze as a 'voice of the city'. She commands Oonishi to kill her for causing the madness in Lux.
She is eventually captured by the Shapes and taken to Kanno. She refuses to merge with him and become his 'sister', so he has her Shaped. When Oonishi kills her 'spirit', Kanno is free to merge with her since she has no more consciousness. Ichise eventually retrieves her from Kanno and lays her to rest where the Elder ended up.