Takashi Natsume has grown accustomed to his encounters with youkai through the Book of Friends, which contains the names of youkai whom his grandmother, Reiko Natsume, has sealed in contracts. These encounters allow Natsume to better understand the youkai, Reiko, and himself. The Book of Friends is a powerful tool that can be used to control youkai; it is sought after by both youkai and exorcists alike. Natsume just wants to live out his daily life in peace but is constantly disrupted by these experiences. If he is to end this torment, Natsume must explore more about the book and the world of exorcism, as well as begin to open his heart to those who can help him.

The movie of Natsume's Book of Friends series. Natsume has been busy, navigating between humans and Yokai when he coincidentally reunites with an old classmate, Yuki. It brings back painful memories of a certain Yokai. Meanwhile, Natsume also became acquainted with Yorie Tsumura, a woman in the memories of a Yokai whose name he had returned. Yorie knew much about Reiko, but now lived a peaceful life with her only son, Mukuo. Being with this family was comforting for Natsume, but apparently a mysterious Yokai has been lurking in their town. On the way back from investigating, a "Yokai seed" that had latched itself to Nyanko Sensei drops into the Fujiwaras' garden and grows overnight into a fruit tree. When Nyanko Sensei eats a fruit that is somehow shaped like himself, he suddenly splits into three!