If you're looking for manga similar to xxxHolic, you might like these titles. All recommendations are made by Anime-Planet users like you!
Kazahaya Kudo and Rikuo Himura are two teenagers who work for the ‘Green Drug Store,' and also rent an apartment above the store. Rikuou rescued Kazahaya from freezing to death on the streets during the winter, and although Kazahaya is grateful to Rikuo for this, the two can't seem to get along. The mysterious Kakei owns the store and Kazahaya often has to put up with the constant teasing of Kakei's friend Saiga. The strangest thing about Kazahaya's job is that he and Rikuo are often sent on "extra jobs" by Kakei, which are different and more bizarre each time. But because he needs the money to avoid ending up on the streets again, Kazahaya never refuses any job offered to him no matter what strange situation he may find himself in. Just what secrets do each of these four men hide, and why is Kazahaya so reluctant to return home?
As in other Clamp works, xxxHolic does cross over into Legal Drug more prominantly, though there are plenty references to other Clamp works such as Tsubasa, Chobits, and CCS. Moreover, the characters of Domeki Shizuka and Watanuki Kimihiro are so very similar to Kudo Kazahaya and Himura Rikuo,(same template but with a more shounen-ai twist within Legal Drug) as they form this duo of supernatural guardian and medium roles. There are tiny variations between both, such as a seemingly innocuous pharmacy run by a man enshrouded by mystery (Kakei and his pharmacy) versus a wish-granting shop run by a witch enshourded by mystery (Yukko and her shop). Both deal with supernatural dangers or tasks that must be completed by the duo, though each series has its own drama and depth.
Both of these manga are about a mostly ordinary boy/teen learning about youkai and other supernatural entities with the help of an older female mentor who is extremely knowledgeable about such things. Nonnonba has a historical setting, and is like a realistic, more down-to-earth version of xxxHolic, which has a bunch of fantasy elements. However, both have very similar set-ups and story progression, so may appeal to the same audience.