Cyfi is a fairly minor character in the book Unwind, but he is significant when he shows the reader the dangers of unwinding and body part transfers.
Cyfi's real name is Cyrus Finch, and the reader is told that he was a "storked" child. That means he was left on somebody's doorstep when he was a baby. It's totally legal and even expected within the book's society. Cyfi's new parents are two homosexual men that raised him. Cyfi has genius level intelligence. He claims that he had an IQ of 155. I say "had" because prior to the events in the book, Cyfi was hit by a car and needed to have his right temporal lobe replaced by an unwind. His IQ has been reduced to around 130.
Having an entire new lobe in his head causes Cyfi some problems. He began to experience feelings, impulses, and memories from the unwound donor. Cyfi would occasionally even change personas completely and begin acting like that donor (Tyler Walker).
By the time Lev meets up with Cyfi, Cyfi is feeling strong urges to go to Joplin. Tyler's personality has almost completely taken over, and is pushing Cyfi to return "home." Cyfi/Tyler makes his way home and begs his (Tyler's) parents not to have him unwound. This is the last time that the reader encounters Cyfi in the book, because Lev chooses this moment to escape and leave Cyfi. Cyfi will later return in a different book in the series.