Madara

Madara also known as Nyanko-sensei is a powerful beastly youkai who more commonly takes the form of a maneki-neko. He acts as Natsume's bodyguard on the condition that when Natsume dies, he will inherit the Book of Friends, thus giving him control over a vast number of youkai.

Despite his continuous complaints about Natsume being too kind for his own good, Madara has grown fond of the boy, and helps Natsume return names to youkai throughout the series even though it will diminish the power of the book by the time it is in his hands.

Appearance
He takes the form of a maneki neko (lucky cat) that is round and cute (at least, according to him, however this also confirmed by Taki). Other characters such as Tanuma, have noted that his head in this form is unusually large. His maneki neko form is white, with an orange and grey marking on the top of his head and back, black eyes, wearing a red cat collar with a gold bell on his neck and has small red markings on his face.

In his original/true form, he is a colossal (so large he can cover Takashi underneath a single paw and his eye is larger than Takashi's head) wolf-like youkai with white fur, red markings on his face, and gold eyes.

Like most youkai, his original form cannot be seen by people with little or no spiritual energy.

Personality
He has a somewhat condescending personality. At first, he only protects Takashi for the Yuujinchou, but as the series progresses, he becomes friendlier with not only Takashi, but Natori, Tanuma, and Taki. His attitude throughout the series can be described as selfish, prideful, and comedic, due to how he acts becomes the usual "gag" of the series.

He does have a very immature and playful side; often drinks himself silly and loves to eat dango(a Japanese snack) and other sweets, making him heavier and rounder.

Despite of his protesting that he is not a cat, he acts exactly like one, li

ke getting excited with cat toys and chasing small animals. He also likes to bully off dogs or throw tantrums.

He has a more caring side to him which he tries to deny or explain away as something else but as the series progresses, it becomes obvious that he is attached to Takashi and is extremely protective of him. Evidence of this is when he went into a rage when Takashi was wounded trying to protect him in Chapter 26 but Takashi managed to calm him.

He is shown to be acquainted with several youkai, like Tsuyukami, Hinoe, and Benio. His strength and rank as a youkai are evident in his interaction with other youkai who are obviously afraid of him, even in cat form.

Trivia

 * Kazuhiko Inoue changed his voice for Madara's cat form in order to fit his form.
 * In Madara's cat form, he gets fatter as the story progresses.
 * Nyanko-Sensei gets several different nicknames from other characters over the course of the series: He is called Nyankichi-kun by Touko, Nyangoro by Shigeru, Ponta by Tanuma, and Nyan-Nyan-Sensei by Nishimoto.
 * Yuki Midorikawa wanted Natsume Yuujinchou to center around a boy and his non-human teacher, choosing between a bird or a cat. She eventually settled on a maneki-neko, which became Nyanko-sensei.
 * Yuki Midorikawa based Nyanko-sensei off of a ceramic maneki-neko statue that was given to her when she was young by an elderly couple who took care of her a lot. She loved it due to its charming face, but accidentally broke it one day. Sobbing, she glued it back together with modeling clay, and it is still sitting at her parents' house today. Midorikawa first drew Nyanko-sensei while trying to remember her maneki-neko's face.