CyFi is a teen that helps Lev when Lev finds himself on the run. CyFi defines words like Lemony Snicket ("Solace—that means 'comfort'" (3.21.3)) and knows how to get people to give him food, so he doesn't have to root through trash. At fifteen, CyFi is two years Lev's senior, and calls him "Fry," as in small-fry.
While Shusterman doesn't get into race relations too much in this installment of the series, we learn that "Umber" is the new word for black people in this world, and no one seems to bat an eye when they discover that CyFi has two dads, not even super-religious Lev.
What CyFi really does is give us a look at the, well, sci-fi aspect of the book—the Unwind procedure, and specifically its effects on the people who receive organs. CyFi receive his "entire temporal lobe" (3.21.47) from an Unwind named Tyler. As a result, Tyler sometimes takes over, like Melanie Stryder in The Host. CyFi is traveling to Joplin, Missouri, Tyler's home, hoping to get some sort of solace and stop the little kleptomaniac from hijacking his brain and forcing him to steal things.
Lev helps CyFi, appalled when they arrive that Tyler's parents feel like they're the victims. We learn at the end that CyFi testifies before Congress about changing parts of the Unwind act. Maybe when they see how a beneficiary can become a victim, things will change.