The song is Wired Life by Meisa Kuroki for Ao no Exorcist. It is a slow and relaxing, good to listen to after all the action from the anime. Though I personally prefer the opening more than this because I think I really enjoyed it. Don't be mistaken, I'm not saying this song is bad. It is still pretty good and it will be one of those songs which will I wouldn't be mind listening to. However the song dis not show its own individuality; which is one of the things I think it lacked.