STATS/PERMISSIONS
Name: Madara. Nicknames include Nyanko-sensei, Nyankichi, Nyangoro, buta-neko, baka-nyanko, nekodaruma, ricecake-cat, Ponta, Nyanyan-sensei and so forth! He will introduce himself as Nyanko-sensei, because giving someone your real name is a big deal in the spirit world.
Age: Unknown, at least a few hundred years. He's basically ageless, and when discussing things with other spirits, he mentions that 'a human life is just an instant' and that 'it passes by so fast that it's scary.'
Height: Varies! He's rather large for a cat, average height as a schoolgirl, and big enough to pin a human down with one paw when he's in his true form.
Eyes: Black as a cat, gold in true form or human form.
Hair: Black, ginger and white as a cat. His hair as a girl is also ginger. His true form is pure white except for red markings on his face.
Medical Info: He's a spirit who can change his form. Very healthy.
Physical traits: Vary! His usual shape is the fat cat--he looks like a manekineko (lucky cat) because he was trapped inside a statue of one for years.
His true form is this. It's not specified what kind of animal he's supposed to be, but since he insists so vehemently that he isn't a cat, it isn't feline. I HAVE LOOKED THINGS UP and I still don't know what type of spirit he is--his appearance and some of his abilities/traits fit a fox spirit, but the rest don't. He might be based on the Raiju.
He can also assume a human form that borrows heavily from Natsume Reiko's! Schoolgirl in an old-fashioned uniform. He has unusual coloring and slit pupils, but otherwise he can pass as normal. He can take other kinds of human forms, but chooses not to do so.
What's Okay To Mention: Anything is fine! Canon doesn't actually have anything you could spoiler him in the face with yet.
Notes for the Psychics: FAT CAT
LIKES FOOD AND ALCOHOL
WANTS THE BOOK OF FRIENDS
WANTS TO EAT NATSUME not really, there's a lot of unspoken affection there
HATES HUMANS BECAUSE THEY'RE WEAK AND SHORT-LIVED not really
Nyanko actually has a lot of depth to him, he just enjoys being a greedy old man in a cat's body.
Abilities: Madara is a high-level, extremely powerful spirit--strong enough to take on almost any other spirit/demon in a fair fight and win. We meet very few who are on his level, and nobody yet who is outright stronger than he is. He's the only one Natsume Reiko ever met whose name wasn't put into the Book of Friends. He's also strong enough to manifest a real, physical body almost all the time, so people can see/touch/talk to him (most spirits don't have enough power to.) We never find out what his exact rank in the spiritual hierarchy is (or what the ranks even are), but he's clearly able to deal with more major mountain/forest/river gods and not just small fry.
He can sense youkai and identify their type and location. He shapechanges. He can blast away hundreds of minor spirits with raw power if he has to. And he also calls down DIVINE PUNISHMENT FROM HEAVEN!11 when he's drunk and pissy--a lot of his powers seem to be lightning-based. He's manifested an additional ability in the second season: if he gets a strong enough hold on a spirit, he doesn't have to devour it completely. Instead, he can just eat most of its power, so its form diminishes greatly and it can't bother anybody for a good long while.
A NOTE: only people with some spark of spiritual power can understand what he says in his fat cat form. Those who don't just hear, 'NYAN NYAN NYAM NYA!'
Kissing/Hugging: HE IS ACTUALLY EASILY TOPPED BY THIS. KITTY WAS MADE FOR SMOOSHING, HE IS FAT AND SOFT AND WARM. He does stink of booze often, though.
Fighting: Like I said, he's one of the most powerful spirits we've encountered so far in his canon! But it takes a major threat to Natsume's life and the Book of Friends, or a straight-out attack, to get him to fight seriously.
Shapeshifting/Bodyswapping/Spitting at/Stepping on: Talk to me for the first two, and the latter two are encouraged for hilarious comedy. He'll leave a frog in your bed as revenge or something.
Maim/Murder/Death: Maybe to the first if it ever comes up. No to death.
Cooking: WHY COOK WHEN YOU CAN GET HUMANS TO PROVIDE YOU DELICIOUS FREE FOOD.