Kekkaishi is perhaps the least-fitting show Adult Swim has picked up in its existence, period. It has its dark moments but is no darker than anything Naruto's done, and Naruto Shippuden airs on Disney XD of all places.
Source:
http://www.adultswim.com/schedule/onair.html Insult to injury: placing it behind the considerably darker and more violent Brotherhood.
I love Kekkaishi but the show just does not work on Adult Swim. It is going to bomb pretty damn badly.