Due to an unusual ability to see strange creatures called youkai, Takashi Natsume has never fit in. Passed around from one foster home to another, he was left isolated and lonely. Over time, he has accepted that no one would ever believe him and has closed himself off to his current caretakers and classmates. When Natsume accidentally breaks an intangible barrier, he frees Madara—a mighty spirit in the form of a lucky cat. Madara notices that Natsume bears a remarkable resemblance to his late grandmother Reiko Natsume, an outcast girl who became known across the youkai world for creating the Book of Friends. It is now in Natsume's possession, along with its power to call upon the written names of the youkai Reiko had defeated. With no interest in its powers, Natsume decides to keep the book for the sake of his grandmother's memories and to protect it from scheming youkai. Therefore, he makes a deal with Madara: he will hand him the book once his time is up, and in turn, Madara will act as Natsume's unofficial bodyguard, nicknamed Nyanko-sensei. With his newfound goal of freeing those Reiko had sealed, Natsume's relationship with both youkai and humans slowly begins to improve. Natsume Takashi has the ability to see spirits, which he has long kept secret. However, once he inherits a strange book that belonged to his deceased grandmother, Reiko, he discovers the reason why spirits surround him. Containing the names of these spirits, a binding contract was formed between the spirits and the owner of the book. Now, Natsume is determined to free the spirits and dissolve the contracts. With the help of a spirit cat, his days are filled trying to return the names to these spirits.