Nyanko Sensei, also known as Madara, is a powerful and ancient spirit in the anime series 'Natsume Yuujinchou'. Despite his small, rotund appearance resembling a lucky cat, he is actually a mighty wolf-like youkai. He becomes a companion and bodyguard to the protagonist, Takashi Natsume, after forming a contract to inherit the 'Book of Friends'. Nyanko Sensei is often seen as a comedic, gluttonous character, indulging in food and drink, but he is fiercely protective of Natsume. His wisdom and strength make him a crucial ally in Natsume's journey to return the names of spirits bound in the book.