definition of a mary-sue

A mary-sue is a beautiful girl who gets somehow drawn into the main storyline. She's usually stunningly pretty, and everyone notices. Most of the time she's either a kick-arse modern chick with an independent attitude and a lust for life or a slender, fragile beauty. More often then not she's got long, wavy hair and deep, glowing pools for eyes. Her appearance in the series is part of her
attempt to resolve some issues that stem from a long ago problem that left her with issues. She comes in, and is instantly swept up into the main storyline, which is a good thing for our characters,
because the Mary-Sue is extremely multi-talented, often most talented in the expertise of our characters. In fact, unbeknownst to every one (including herself), she holds the key to solving the main problem our characters face. Her proficiency stems from her dark past, which is in some important way connected to the present problems. As the story unfolds, she must deal with her issues as she leads the heroes into victory against the almighty foe. Along the way, her charm will be noticed by one or more of the series' bishe (hot guys, for you non-anime people), who will usually discard the
romantic tension he had with some female character to fall hard for mary-sue. After the fight is over, he and her will ride off into coupledom together, or she will die in a blaze of triumph in the final battle, leaving her man scared, but a better person for having known her. Sometimes, both will die for their love, leaving the others to lament.

two: The problem with ooc is not that the audience is shocked by that character's break from cannon romance or the goofy things they do for love. The problem is that, too often, these stories become
formulated, with everyone going grossly out of character in order to pay homage to the new girl. Lots of times, the fandom comes to a point where the only kinds of stories posted are those like this. This gets really boring.

There's a difference between a well written female OC and and Mary-Sue. You can tell a Mary-Sue because she's so perfect, and any mistake she makes is little more than a ploy to get the characters
to gather and support her. In short, a Mary-sue story revolves around the Mary-Sue. A well-rounded OC story revolves around the series' characters.