Natsume's Book of Friends centers on Takashi Natsume, a teenage boy who has inherited the ability to see spirits, or yokai, from his grandmother Reiko. This ability has isolated him throughout his life, as others perceive his interactions with invisible beings as strange or unsettling. After moving to a rural town to live with distant relatives, Natsume discovers a mysterious book called the "Book of Friends," which Reiko created decades earlier. The book contains the names of numerous yokai she defeated in challenges, binding them to her service. However, Natsume learns that these yokai are now bound to the book and seeks to return their names, freeing them from their contracts.

Accompanying Natsume is Madara, a powerful yokai who takes the form of a rotund, cat-like creature and often goes by the name Nyanko-sensei. Though initially motivated by the promise of inheriting the Book of Friends after Natsume's death, Madara becomes a reluctant protector and guide, aiding Natsume in navigating the complex world of yokai. Together, they encounter a variety of spirits, some benevolent and others malevolent, each with their own stories and connections to the Book of Friends.

The series unfolds episodically, with each arc or episode focusing on Natsume's interactions with different yokai and humans. Many yokai seek to reclaim their names, while others attempt to steal the Book of Friends for its power. Alongside these supernatural encounters, Natsume gradually builds relationships with the people around him, including his kind foster parents, Touko and Shigeru Fujiwara, and classmates like the empathetic Taki and the exorcist Natori. These relationships help Natsume overcome his loneliness and find a sense of belonging.

Themes of empathy, understanding, and the coexistence of humans and yokai are central to the narrative. Natsume's journey is one of self-discovery, as he learns to reconcile his unique abilities with his desire for a normal life. The series balances moments of melancholy and introspection with warmth and humor, creating a poignant exploration of human and yokai connections. Through its episodic structure, Natsume's Book of Friends weaves a rich tapestry of folklore, emotion, and personal growth, anchored by its protagonist's compassionate resolve to free the spirits tied to his grandmother's legacy.