>>2 I read and finished Tsubasa before I read xxxHolic,and while they do make reference to each other, they are not completely vital, especially in the beginning. For later parts of xxxHolic it is very helpful to at least know what happened in Tsubasa, but no matter what there will be at least a little mind fuck. I recommend two read them both, and if Tsubasa doesn't look that appealing at first try to read some of it because it changes in a big way. moral of the story, they are both amazing