Yūko receives an invitation for the opening of an auction from a mysterious unknown sender. Likewise, fanatical collectors are summoned to an old mansion whose owner doesn't make an appearance. One after another, each collector disappears and a number of other strange occurrences happen during the night. The questions of what exactly it is that's being auctioned and who the owner of the mansion is must be solved in order for Yūko and Watanuki to get to the bottom of this.

[Source: Anime News Network]

Watanuki Kimihiro is a high school student plagued by youkai and ayakashi, spirits with a strong attraction to him. The spirits are invisible to others and encounters with them are extremely troublesome. When he stumbles into a shop that grants wishes, however, events in his life promise to become more unusual.

The shop is owned by Ichihara Yuuko, a mysterious and beautiful (sometimes playful) witch of many names and esoteric renown. For a price, she offers to grant Watanuki's wish to be rid of the spirits. The price, according to Yuuko, must be of equal value and so, as payment, he temporarily becomes Yuuko's part-time employee.

Watanuki's job consists of small errands dealing with the supernatural and household chores. His love interest, Kunogi Himawari, and "rival", Doumeki Shizuka, occasionally join him in his work as per Yuuko's request. The three become increasingly close despite Watanuki's annoyance with Doumeki.

[Source: AniDB]

Still working to get his wish complete, Watanuki finds himself into more mess than he can handle when certain facts about his everyday life gets revealed and when he needs to learn the lesson of Yuuko the hard way.

[Source: Anime News Network]

While following strange dreams, Watanuki meets some old friends & solves a riddle. These dreams eventually tie into another mystery involving Li Syaoran and Watanuki's importance in the world of xxxHOLiC and Tsubasa: RESERVoir CHRoNiCLE.

[Source: Anime News Network]

Yuuko's time flow finally starts moving again, after being alive for an unknown amount of years she must depart now since she can't be hold by the world of the living any longer. During her final moments she faces Watanuki, her loyal servant and friend and makes her final wish, "stay alive". So Watanuki made the promise to remain in the store of the wishes until they meet again. Many years later he still keeps that promise giving hope but also taking important belongings from those who ever come to him to make a wish.

[Source: Anime News Network]