Watanuki Kimihiro is haunted by visions of ghosts and spirits. Seemingly by chance, he encounters a mysterious witch named Yuuko, who claims she can help. In desperation, he accepts, but realizes that he's just been tricked into working for Yuuko in order to pay off the cost of her services. Soon he's employed in her little shop - a job which turns out to be nothing like his previous work experience!
(Don't forget to hide discussions in spoilers if they reveal anything major that happens later in the series, in case anyone hasn't completely read it yet)