Xander is best friends with Willow and Buffy. He has known Willow since childhood. He has no special abilities but is considered to be the heart of the "Scooby Gang", the glue that keeps them together.
"Working with the Slayer. Seeing my friends get more and more powerful. A witch. A demon. Hell, I could fit Oz in my shaving kit, but come a full moon, he had a wolfy mojo not to be messed with. Powerful. All of them. And I'm the guy who fixes the windows."