Fans of xxxHolic will want to check out episode 17 of Kobato. for an interesting 30-second cameo. What follows is sort of spoilerish, so I am putting it below the fold:

Ginsei delivers a box of baumkuchen to what appears to be Yuuko’s shop. There is no sign of Yuuko though. Instead he is greeted by a surprisingly calm and cheerful Watanuki, dressed in some sort of tail-coated uniform with a quarter-moon ornament.

“So you’re a part-time worker then?” says Watanuki. “I’ve had three part-time jobs myself. I was terribly abused by a selfish shopkeeper….I was also at this labyrinth-like place. It was another really weird location with lots of strange rooms…”

That suggests to me that Yuuko has left and Watanuki has taken her place. If so, maybe the underlying story of xxxHolic is about Yuuko grooming Watanuki to be her successor.