Urihime is one of the three faithful youkai under the command of Natori Shuuichi. She first appears with Sasago. In recent times, she is often seen appearing with Hiiragi under the command of Natori-san. All three of them have pledged their faithfulness to Natori-san. 

Natsume has always been an outcast because he inherited his grandmother's ability to see yokai. After moving to his grandmother's hometown and accidentally releasing a yokai imprisoned in a Lucky Cat statue, he learns about his grandmother's "Book of Friends," which contains the names of the yokai she defeated, and allows its wielder to command the yokai named within. Since then, yokai now visit him on a daily basis, seeking to either get their names back or take possession of the Book of Friends. 
(Source: NIS America)

The fourth season of Natsume Yuujinchou. 
 
Still in possession of his grandmother's Book of Friends, Natsume spends his days returning the names of yokai to their rightful owners. He has been learning how to deal with the yokai and humans that surround his life, but the time has come for him to deal with something even more difficult — his own past, and future. 
(Source: NIS America)

When Reiko was Takashi's age, she bound the names of demons and spirits in her Book of Friends, enslaving them to her capricious whim. Now Takashi is the owner of the book, and the creatures will do anything to get their names back.
 
(Source: Viz Media)

The fifth season of Natsume Yuujinchou.

The sixth season of Natsume Yuujinchou.

The seventh season of Natsume Yuujinchou.

The film features an original story written under Midorikawa's supervision. 
 
(Source: Anime News Network, edited)