Who is Christopher from Airhead #2: Being Nikki and what is their importance?

An old friend of Em's, Christopher demonstrates several sides of his character in "Being Nikki." The first is the friendly, laid-back guy that Em knew when she was still in her old body. He is good-looking geek who loved to play video games with her. However, as the novel progresses, he reveals what Em thinks of as his "supervillian" side. This side emerges when he is being protective of Em and specifically when he is trying to avenge her death. He has planned to do this by using his strengths and hacking into Stark Corporation's website to bring the company down. Though it takes him some time, Christopher eventually catches on to all of the hints the "new" Em is sending him, and realizes that she is still alive, just in the form of Nikki. Nevertheless, he's completely willing to help her solve the mystery of Mrs. Howard's disappearance, and continues to investigate with her. Therefore, he is shocked and confused when Em breaks up with him at the end of the story, on the same evening when they've finally gotten together, in favor of Nikki's ex, Brandon.