Not So Weak

Someone who is Not So Weak is shy and a natural target for a bully. The person looks harmless. You, as the bully, think that you can just walk all over this person without their raising an objection. And you will find you're right.

Go ahead, take their stuff or break it. They won't stop you. Are you angry at them? A scolding or outright abuse is bound to be effective—they have little self esteem. This person simply can't or won't defend themselves.

And yet. They tolerate it if you hurt them; but if you hurt anyone else, and they see you, then they're not going to stand for it. They will step in. Humankind is their Protectorate.

This person places no value on themselves, but they will do whatever they can for anyone whom they feel needs help. They'll usually avoid outright violence, thus maintaining the appearance of weakness. But they will sometimes use violence (proving themselves Not So Weak) to protect a loved one or Innocent Bystander. They just will never feel the need to protect themselves.

May overlap with The So-Called Coward, but not always. The So-Called Coward simply avoids fights of all sorts, except for the ones with the highest stakes. Someone who is Not So Weak does not believe they themself are worth defending, and is more likely to end up either as a punching bag or as the person esacalating a fight involving someone else. Or both in turns.

Often overlaps with Cowardly Lion. Compare Mama Bear for an example with a more specific Protectorate involved.

Anime and Manga

 * Subaru in .hack//Sign, who founded the Crimson Knights to help the admins uphold peace in The World but is nearly scared into submission by a single stalker like fan. And then she kills said stalker—despite being under-leveled—so she can get to Tsukasa.
 * Kenichi: The Mightiest Disciple is essentially defined as someone who is a coward on his own but will not stand for slights or attacks against his friends. Or enemies.
 * Chad in Bleach, though this is not because he is afraid to fight so much as because of a promise with his grandfather and to himself that he would not fight for himself. Presumably he fears becoming too violent and wild again.

Chad used to be a bully himself when he was younger, until he saw the example of his grandfather who took a beating for him by vengeful parents/guardians of the children he tormented. Chad's grandfather is now dead, and to in respect to his memory, he promised never to fight for himself.
 * One Piece:
 * In the very first chapter (fourth episode in the anime), Luffy's pirate idol "Red-Haired" Shanks allowed Higuma, a small time mountain bandit, to thoroughly abuse him and casually laughed it off after the fact. When Higuma came back later and threatened Luffy, on the other hand, he learned Shanks and his crew were not to be taken lightly.
 * Shanks' Number Two Ben Beckman stated if one makes the mistake of challenging them, they could at least have the courtesy to bring a battleship.
 * Luffy would later emulate that example with Bellamy in Mock Town and will generally not worry about someone unless they're threatening his crew or otherwise obstructing his path.
 * Pick on Baccano!'s Jacuzzi Splot, and he'll lie down and take it. Beat the crap out of him, and he'll insist it was his fault. Kill him, and he'll probably have it stipulated in his will that no harm shall come to you. Hurt any of his True Companions and, well, you're fucked.
 * Ren Kannagi from Kaze no Stigma is a sweet kid who never wants to hurt anyone-unless you take a swing at his friend and then he will slam a boy taller and stronger than him against a wall with a murderous expression on his face. Not to mention he's a member of the Kannagi family whose standard operating procedure for evil spirits is Purify It With Fire.

Comic Books

 * During the high-school years, Spider-Man knows he could knock bully Flash Thompson into next weekend, wait until next weekend, and then kick him right back. He knows that with a bit of restraint, he could even do it without compromising his Secret Identity. However, because with great power Comes Great Responsibility, he refuses rather than risk harming him, even though he feels the humiliation of constantly backing down from him. Of course, being a Superhero, protecting the innocent is how he spends his afternoons.
 * Young Avengers: Wiccan of the Young Avengers was the target of a bully before becoming an Avenger and wouldn't stand up to the bully for himself, but when the bully found a new target he laid down the smackdown.

Literature

 * Nita in the first Young Wizards book. Character development gives her more self confidence by the end, but several books later she still retains many of the same character traits.

Video Games

 * In Knights of the Old Republic, Mission Vao first met Zaalbar as he was being harassed by a few Rodians. He ignores them until Mission yells at them and gets promptly smacked to the floor... At which point he beat them to a bloody pulp. The two have been best friends ever since.

Visual Novels

 * Masayuki in A Profile is an occasional victim of bullying, generally passive in his interactions with others and an unfailingly nice person, leading him to be taken as a lightweight. However, in the past, he was a feared street fighter and can be very scary. What's pretty much the only way to make him mad? Threatening his little sister, which gets him so angry and scary that an entire gang backs down and tells him what he wants to know.
 * Mai in Kanon, who never defends herself or explains her actions but is so kind that she's willing to let a dog try and eat her hand because she has nothing to feed it. After defending everyone around her from being attacked by it. Who then proceed to mock her.
 * Nagisa in Clannad, who won't even let Sunohara go undefended. The only one in the cast who tries to say nice things about him as well.
 * Sakura Matou and Shirou Emiya in Fate Stay Night, for different reasons.

Western Animation

 * Parodied in The Simpsons with "Undercover Nerd" with Rainer Wolfcastle. Wolfcastle is a Schwarzenegger Expy, with the giant, muscular physique that entails.
 * Fluttershy from My Little Pony Friendship Is Magic. She is the ONLY adult character to be bullied effectively, but is still capable of Talking the Monster to Death with her verbal and body-language-based shaming, known as The Stare.