Original characters are exactly what they sound like, characters in a fanfic who are created by the fanauthor herself. They are used in almost every single story, and sometimes work very well. Other times, they suck. I have very strong opinions on the use of OCs, which I realize many people disagree with. That said, based on my own experiences as a reader and writer, I feel like I've come up with a fair objective list of ways that OCs can be developed to work well within stories.

So first, here's a list of pros and cons that I've discovered to writing OCs.

PROS
* Original characters are a necessity for nearly any romance that isn't slash
* Original characters give you a chance to play with the world outside of what is presented in the movie
* Original characters give you more of a feeling of ownership to a fic, because they are developed entirely by you

CONS
* It is very, very hard to write an original female character (for a romance or otherwise) who fits into the world of 1899
* Many, if not most, original characters are cliches
* Too often, original characters take over stories by become Mary Sues or Gary Stus (more about them later), a situation which takes the canon characters out of character and take over the story in a very bad way

Again, these are opinions. I understand why people choose to use original characters, though I generally advise against. I, like many people in the fandom, am interested in fanfiction because of my love of the canon characters. I'm not interested in stories that revolve around characters not in the movie, and, while I enjoy a good romance, I'm only interested in ones that are about the boys I love, not that center around a girl I've never heard of.

Furthermore, as I mentioned, it's hard to create a OFC who's not anachronistic in 1899. Most of us have very modern mentalities about women; it can be both frustrating and difficult to write about Victorian women—but they were, quite literally, Victorian. That means that women always wore skirts, that contact between genders was heavily supervised, that women and men had very different, very specific spheres (women inside the home and men outside of it), and that most people were somewhat religious.

Her are some historical fact ground rules for working with female characters in fics. These are, as I said, facts; part of the problem with many OFCs is that they completely ignore these basics, and thus warp the world around them, and turn into Mary Sues. (More on those in a minute.)

Fact: There were girl newsies. Not a lot of them; about one in every eight to ten newsies was female. And, as they got older, many of these female newsies became prostitutes to pay the bills.
What it means for your fic: Your OFC can not be the only girl newsie in New York, nor in any borough. Nor will she be the only girl the male newsies have ever met.

Fact: Lodging houses were run by religious charities, and lodgers were obligated to adhere to very rigid rules of behavior (no smoking, no swearing, and strict cleanliness). There was also a historical lodging house for girls.
What it means for your fic: Your OFC will not be the only girl in an otherwise all-male lodging house. Young, unmarried boys and girls were not allowed to socialize together without chaperones. If your OFC is brought to the boys' lodging house, rather than being invited to stay there (which would have been unspeakably scandalous), she would have been directed to a girls' lodging house.

Fact: Women of all ages wore skirts. Every day.
What it means for your fic: Your OFC should not be wearing pants; not even if she's a tough, tom-boy newsie. The historical female newsies wore skirts, because all women wore skirts. No one would think to do otherwise. In some places, it was even a law that women could not wear pants. (Furthermore, these skirts were long, ankle or floor length. Hemlines didn't rise until World War I, where fabric shortages made shorter skirts a necessity.)

Fact: Men and women had very different, very rigidly defined social expectations. Most women (not all, obviously, but many) wished to get married and have children; and even those who didn't wish to do so were expected to, anyway. Society was, quite literally, Victorian.
What it means for your fic: Presumably, street kids had more freedom than those who weren't working for a living. However, if your OFC is middle or upper class, so much as being alone with a boy was scandalous, and would destroy her reputation—let alone kissing or doing anything further without first being married. Dates would be chaperoned by an adult; dating a newsboy would not be allowed. And most daughters would not defy their parents to do so anyway, not even for the most charming newsboy in all the city. (This is a commonly used plotline, and can certainly work; however, think long and hard about the historical circumstances before attempting it.)

It's also worth noting that women were expected to never smoke, drink, or swear in public. I think it's safe to bend the rules, when dealing with girls in the streets; but the historical circumstances should be kept in mind in order for a fic to make it read realistically, and avoid having a Mary Sue.

And now (cue ominous thunder roll) what is a Mary Sue?

A Mary Sue is a character in fanfiction who is often (though not always) an idealized version of the author herself. (Her male counterpart is called Gary Stu; often, in this fandom, newsboys come to resemble him, not as inserts of the author, but as the author's idea of a perfect, fantasy boy.) Mary Sues are characters who are larger than life, and thus definitely too large for fanfic. What they do is warp the canon world to their will, making everything center around them.

Everybody who meets Mary Sue instantly adores her—except villains, who instantly hate her. And why shouldn't people adore Mary Sue? She's invariably beautiful, kind, generous, sweet, even-tempered, and cartoon bluebirds braid her hair for her every morning... Or, alternately, she's a fiery feminist, who's loud mouthed, not afraid to say what's on her mind, can punch out any guy who approaches her, defends the weak, etc. She can take many other forms, actually, but these are the two most common in this fandom.

The problem is that Mary Sue takes all of those character traits and combines them to create a monster. Mary Sue isn't just a nice girl with pretty eyes and a lovely singing voice, she's a perfect character. She never does anything wrong, and she's good at everything she tries, the very first time. She's the best at everything she does, too. She's smarter than David, better with a slingshot than Spot, a better gambler than Racetrack, and a better leader than Jack, and she charms Skittery out of his bad mood. She's also often a canon newsie's long-lost sister, and another one's love interest. She's never, ever wrong. If she died, the newsies would never recover. They'd do anything to save her.

Are you beginning to get the idea? Everything about Mary Sue is perfect, and that makes for a really lousy character. For one thing, it's because no one is perfect. Not a single person. Everyone has flaws, everyone gets in bad moods occasionally, everyone makes mistakes. That makes her horribly uninteresting to read about, because it means she can't develop at all as a character, and every character in a story should develop.

Let's compare this to the movie itself for a moment. Jack Kelly is charming and gorgeous, and the movie is all about him. But he's not a Gary Stu. Jack is not perfect, despite being charming and gorgeous; he has flaws. He's a liar, even lying to the people he cares about the most, and he's selfish, as we see when he's willing to go scab. And, through the movie, Jack grows and develops as a character. He learns that he can't be so selfish when people are relying on him, and comes back to the strike. He also grows up, and discovers that he can make his own family, rather than living in a dream world—that's why he stays in New York, instead of running off to Santa Fe.

So Jack's got flaws. So do the rest of the characters: David may be smart, but he has no street smarts at all; Spot's a violent punk; Racetrack's got a mouth that could easily get him in trouble, and he seems to consistently lose money gambling. No one is perfect, and so OCs shouldn't be, either. Having flaws leaves rooms for characters to develop, and that development is often the heart of a story.

You can spot a Mary Sue pretty easily. If the canon characters are acting a little out of character, or being beaten at their own games, or are obsessed with a girl they just met, there's probably a Mary Sue around. If the story has terrible grammar, no punctuation, and you can't figure out the spelling, but there's a girl running around, she's almost certainly a Mary Sue.

The line between Mary Sue and OFC is very fine, hard to see, and easy to cross. So how do you avoid writing a Mary Sue?

First, look back at the historical guidelines section. Most Mary Sues have no regard for history at all. Women wear pants and punch out guys in the street—but they do it with no consequences. No one shuns them, no one points and laughs or calls them a hussy, no one so much as bats an eyelash. That's Mary Sue's evil powers at work, warping the world around her to her whims. All character actions should have consequences, and that includes when it comes to historical context.

Next, consider her flaws. As I said, everyone—and every character—has flaws. OCs should too. And you have to be careful when deciding what flaws a character has. Consider her background (and yes, you should know her background) and find flaws that make sense based on how she grew up. New York is a busy, crowded city; and at the turn of the century, many poor people were crowded in tenements. Maybe having grown up crowded in a small room means that she's claustrophobic, and will panic if she's in a small, cramped room. Or maybe it means she gets really cranky when she's forced to spend too much time with others, and not enough alone.

The important thing about these flaws is that they are flaws, and have a negative impact on the character. A very common Mary Sue flaw is, "too stubborn." However, this is not used as a flaw with a negative impact; instead, it's a way of saying that Mary Sue is never wrong, and gosh darn it, she'll fight to defend herself and all she believes in... and win, each time. That's not a flaw, it just makes her perfect again. Instead, a flaw would be if her stubbornness gets her into fights she can't win. She's wrong, but too stubborn to admit it; she's defeated, verbally or physically.

That defeat is another key to avoiding a Mary Sue, and it ties back in to what I was saying earlier. Character's actions should have consequences. Mary Sue's actions often don't, unless that consequence is to make everyone love her. She can get into a fight with anyone, and always win; and afterwards, there are no hurt feelings or anger towards her, no one has any lingering resentment. There are no consequences. If she's caught in a lie, she's forgiven instantly. If she makes a mistake, she's forgiven instantly. No matter what she does wrong, she's always, always forgiven. Which means her actions have no consequences, which again, means she's a poorly written character.

Finally, the last major key is this: make sure the characters who surround your OC are, in fact, in character. That means that if Mary Sue has been lying to them and they find out, they should be angry or upset, at least for a time. It means that the character shouldn't get a free pass just because you, the writer, know she's trying to do the right thing; and especially not because you, the writer, love her so much. You are not the other characters, and if you love your OC so much you can't stand to give her flaws consequences, you are definitely writing a Mary Sue.

I realize these guidelines sound a little hard to follow. They can make it harder to come up with workable plots, and require more effort to keep the characters in character. However, in the end, it's worthwhile. It makes your writing much stronger, your character more realistic, and your readers much happier.