It's funny that despite messing up my OCs, in my first fan fiction stories, I have always seemed to be able to keep the canon characters in character, or at the very least they were recognizable as themselves, so it seems a little weird to me that it just doesn't just click for everyone else. Usually I can just read or watch a series and be able to empathize with the canon characters so well, that writing them in stories seem to almost come naturally. Almost. Some characters are hard for me to identify with, and because I haven't really seen any guides specifically for keeping canon characters in character, I thought I'd give a few tips of my own, especially for these characters that are more difficult to get to know. Of course everyone would have their own interpretation of said characters, and maybe my tips won't work for you, but I thought this could help at least someone out there. Who knows? Maybe this will inspire you to come up with your own tips that you would also like to share with other fan fiction writers.
For those of you new to fan fiction, canon characters refer to characters that are officially in the fandom's universe, and they are one of the biggest reasons as to why fan fiction is written as well as read, so it almost goes without saying that you'll get a load of respect by other fans if you keep these official characters in character. Even for someone who writes with Original Characters (OCs), characters that a fan makes up him or herself to be added into the fan fiction, as main characters, I always look forward to reading about the canon characters first before anything else. That being said, there can be exceptions for keeping canon characters in character, but before I get to those, let me first give you a few tips on keeping the canon character in character.
Before I go on, I thought I would let you know I exclusively write CanonxOC romantic pairings, so you can definitely tell I look forward to romance! However there are times where I personally feel that the canon character may come off as too out of character because of these deep feelings. When it comes to my own writing, there's a reason why I don't write about just any canon character either when it comes to romance or just any genre period. Hence my first tip:
Learn to Like the Character(s)
I can't fathom a reason as to why anyone would write with characters they don't like as main roles. It's OK if you don't like a certain canon character, even if you don't have a specific reason as to why, but I've found that if I don't like the canon character, then I lose steam for the story and end up not wanting to write it even if I write the canon character well. This can be especially problematic if you had advertised that you take requests, and someone requests you to write a canon character that you hate. Of course you could refuse, but you can also take up the challenge, which is why I phrased the first tip the way I did: learn to like the character.
Personally, I tend to strongly dislike loud characters such as Naruto Uzumaki (Naruto), Black Star (Soul Eater), Natsu Dragneel (Fairy Tail), Monkey D. Luffy (One Piece), Tamaki Suoh (Ouran High School Host Club), Ichigo Kurosaki (Bleach), Takeru Manabe (Fruits Basket), Finn (Storm Hawks), Odd Della Robbia (Code Lyoko), and so many more. You can very well call it a personality clash, but even though I don't tend to like these characters, I can find things in them that I can admire and like in which I can keep in mind when I write these characters from either a small scene to having a bigger role in the entire story.
When I first watched Naruto, I found the main character, Naruto, quite annoying and became eager to watch the other characters, but after watching it again from beginning to end, I could see how much he grew and developed, and I understood his motivation and goals much more clearly. The same thing happened with Ayame Sohma from Fruits Basket, and other characters from other series. The more I watched or read the series, the more I got to know the characters, even if I had already finished the series a dozen times.
So watch or read the series again in its entirety and focus on that one or those few characters. If you can't find any qualities that overweigh your dislike for this character, I would advise that you don't take up that challenge and politely refuse the request. Of course if you still wish to take up the challenge, go ahead. It's not like this is my only tip.
There's another reason why I say to rewatch or reread the fandom, which leads me to my next tip.
Get to Know the Canon Character in the Canon Universe
Before you start your fan fiction, rewatch the show or reread the books so the characters are fresh in your mind. Sometimes, if we haven't read or seen the fandom in a while, we can forget the little things that makes the character the character. In addition, if we've read fan fiction in between those large gaps of time, we can meld other people's interpretation with our own, and sometimes this new interpretation isn't as in-character as you may like for it to be when you reread your own writing some time in the future.
You have no idea how many fan fictions I've read where Yoko Kurama from Yu Yu Hakusho was made out to be a lech (embarrassingly, me included because I wrote the story before I finished watching and reading the series). Well, I finished the anime and the manga, and not once did he seem at all perverted to me what so ever. Maybe there was light flirting at one time, but I don't think he was an all-out lech. This "pervert" type of character seems to be tacked onto characters that aren't so well-known or doesn't have as much screen time as other characters, and I can attest that Yoko isn't the only victim of this (Kankuro from Naruto is another character that comes to mind), and yet it persisted because he turned out to be so popular.
Also, where the heck did Gaara (Naruto) liking chocolate chip cookies come from? I remember this being a fanon thing that came in a huge wave, and not once in the manga did I see Gaara even hold a cookie, much less have an opinion on the specific kind of cookie. There was also Hiei from Yu Yu Hakusho liking a specific kind of ice-cream (which I forgot) that also became a fanon wave of it's own. Of course, there's also L from Death Note and strawberries. He likes anything that's sweet, even ham on melon (although he didn't eat the ham), but people continually associate him with strawberries as his favorite food even though he never stated as such (as far as I can remember). I don't mind that Gaara likes cookies, or Hiei likes ice-cream, or L's favorite sweet thing could be strawberries, but they became a huge thing that there was at least a mention in practically every fan fiction I read for a good while years ago. (The L thing is still mentioned occasionally.)
And while you're at watching or reading, you may as do the next step.
I like writing down their lines. This way I can get a feel to how they normally speak, and it can remind me of how they would act in different kinds of situations which would give me an easier time guessing how they would act in the situations I would put them through in my own fan fiction. I actually take note of the entire conversation so I can see exactly what the canon character is replying to, but sometimes the conversation isn't needed.
For example, while Stork from Storm Hawks is well-known to be pessimistic, he isn't like that all the time. Actually, that pessimism isn't even half of who he is. He can be quite mischievous, and when push comes to shove, he can fight back in his own way. His use of sarcasm and quick wit is spot on, and when he's inside his ship, he can't seem to be beat. Not to mention that there were times that his stress or anger was so intense, he had quite the personality change, such as in the episodes "Leviathan" and "Payback." Something that's also frequently forgotten is his knack for his on-the-spot poetry and songs, such as in "King for a Day," "Terra Neon" and "Calling All Domos." Also, did anyone else notice that he seems to like making jabs at Finn specifically, such as destroying the puzzle cube and breaking Finn's rock vinyl, while he treats Junko, Finn's best buddy, more kindly even though Junko also sometimes likes to poke fun at him? All in all, he's actually quite braver than what most people give him credit for and he is not permanently attached to or has an umbilical cord with the Condor, the Storm Hawk's carrier ship, even if he prefers not to leave the ship.
In the Storm Hawk's case, this script note method also helps because Stork knows a lot about these different creatures that this universe houses and Piper knows, well, almost everything else. So this helps me out with the universe also.
This method would also be super helpful for those characters that hardly speaks because this would physically remind you that the character isn't mute, and it wouldn't be out of character for the character to say something if the situation calls for it. It would help you figure out the pattern for when these characters actually voice out their concerns or opinions. For these quiet characters it would be helpful to also state what they are doing instead of speaking, or just actions in general.
Of course this would be helpful for those talkative characters that can go on and on about nothing. May I remind you of Fruits Basket's Ayame Sohma and his long and run out story when the simple point was that Shigure had told him about something or other? The script method can help reveal which types of descriptions these characters like using and can help you imitate this long and unending dialogue.
Another thing to keep in mind is the original dialogue before the translated versions come up. This is especially true for anime and manga. For example, in Soul Eater, Crona's gender is never disclosed, and even Atsushi Okubo says that he doesn't know although he purposefully wanted the gender to be ambiguous, and so is completely androgynous. In fact, Crona usually uses the word "boku" which is "I" in english, but while it is commonly used by boys, it isn't exclusive, so either gender uses it; however, FUNimation and Yen Press had to settle for "he" because using "it" would be offensive. Of course there are also theories as to Crona being genderfluid or intersex, or the Ragnarok experiment wreaking havoc with his identity and hormones or whatever, but those are theories. Just look a little into the original language the fandom uses, because it can sometimes play a part or answer some questions the translated versions couldn't quite explain or misses.
Create your own personal character sheet for the canon character complete with physical description (especially those pesky eye colors for the one time this description is needed), likes, dislikes, habits and just about anything else you can think of, and remember: it's always best to look at official canon sources for this kind of information whether it be from the book, the DVD, or even the official website. Some manga has little extras that reveal this sort of extra information, such as height, but if there is no official information, there isn't any.
I just do not trust any site, such as Wikipedia, that allows anyone to just log in and change information just like that, but I'm not saying that you can't come up with your own conclusions either. I've seen a fan-made website saying that Merbs from Storm Hawks may be amphibian and lives in caves, and while I'm highly skeptical about the amphibian part, it's not like I have canon material refuting it either. Still, I think it would be best to separate fanon from canon and come up with your own conclusion.
Make Use of Astrology
OK, I know not everyone is into astrology or even believes in it, but I do, and this really, really helps me. If the canon character really does have a birthday, make use of it and add onto that character sheet you may have made in the previous tip. Even if you don't believe in astrology, why not try it out? Make a list of the positive and negative traits in each sign, think of the canon character and check off which traits apply. You can also make a journal and write down notes for each sign. Tumblr has some awesome blogs like zodiacmind, zodiacspot, zodiac-maniac (whom are my favorite), which post tidbits about the signs that may be not so well known, or that busted the stereotype each sign tends to have.
Of course I know that astrology is more than just your sun-sign—the planets, houses, asteroids, modes, elements and other stuff also play a huge part in the overall interpretation of a natal chart—but it's not as if every character's exact birthday (month, day and year) along with the time and location is revealed. Actually, almost no fictional character's birth details are included anywhere. I don't even go that far because even I feel that may be too much information, but the sun signs alone can be more than enough of a hint to get to know the canon characters.
Although it can be especially tough if the canon character's birthday lies in between zodiac signs, in other words they're in the cusp. In that case, you have two signs to work with. Kyoya Otori's from Ouran High School Host Club's birthday lies in the cusp of Scorpio and Sagittarius, but he totally fits the Scorpio sign way more than the Sagittarius, so most of the Scorpio posts help a lot. Then again, Jushiro Ukitake's (Bleach) birthday is also a cusp of Sagittarius and Capricorn and I'm pretty torn. In a lot of ways he fits both signs, so taking these notes, which traits fit him and which don't, really help, and it helps me understand how he may think or feel in certain situations . . . such as in the romance aspect of life, which makes CanonxOC pairings so much easier on me.
Now what if the canon character doesn't have a known birthday? Well that really sucks because I would love to celebrate my favorite character's birthday, but if they don't have a birthday, they don't have a birthday canonically. You can either skip this tip entirely, or you can take notes on astrology and choose a sign that fits them. It can still help. The birthday itself isn't as important as the personality and behavioral traits that comes with it and that's what this tip mainly focuses on.
If you really oppose using astrology, you can make your own list of personality traits from a huge list of key words and make your own notations on each of those traits such as in what situation does this character become shy versus when he or she is confident or fights back.
That's about it for the practical tips in order to keep a character in character, but that doesn't mean that there isn't any wiggle room for your personal interpretation, or if you would like to make some changes to the canon character. A little change is fine as long as the character is still recognizable as themselves. That being said, technically you can make any change you want (except for Real Person Fan Fiction which could be considered libelous), but these tips are aimed towards what most people look for and have more possibility that the story would be enjoyable. So here are a few changes that are generally accepted (but keep in mind that there are always one bad apple in the bunch).
There's a story type or warning dedicated to just this, and it's called slash. This is when a straight canon character is written as gay, or bisexual, or other orientations that isn't heterosexual. Sexual orientation doesn't usually change personality types.
I haven't seen any confirmed LGBTQA canon characters written as straight, and there's no official story type or warning label specifically for this situation, but I have seen "het" used to indicate the OC is the opposite gender as the canon character. (This is usually because OCs are usually female, thus the canon character is usually male, but when the canon character is female, sometimes OCs are assumed to also be female unless stated otherwise, so that's why "het" is sometimes inserted in tags.) Some people may not like this because officially canon non-heterosexual characters aren't presented in official media as often, but, well, I don't care at least. It's fan fiction and it's not going to change the canon material in any way whatsoever. I haven't actually seen this before though.
This can be a little iffy, and it mostly depends on the character and how the story is written. Still, even in the most extreme cases, if "OOC" is clearly stated somewhere, it should be fine. If the character was born the opposite gender from the canon, or was somehow mystically changed into the opposite gender, then "gender-bender" would be more appropriate.
Now if you wanted to write the canon character as wanting to go through the transition from male to female or vice versa, or want him or her to be genderfluid or be androgynous, that's a little different, and it makes it harder that there's no official warning or story type for this that I can think of. I would personally find it hard to believe that someone like Zaraki Kenpachi from Bleach would willingly wear a dress, no matter how much you changed the universe and the character's past, and because this would be extremely against his character, I probably wouldn't read the story because it's so OOC. If the change is going to be as drastic as that, you could just call the story a comedy or parody, and it should be fine overall along with stating that the character is "OOC", but not everyone is going to know what "parody" is (for that bad apple who is quick to rant in the reviews before looking more carefully).
In Naruto, what if Itachi never killed his clan members? I can guarantee that Sasuke wouldn't be the brooding jerk he's so well-known to be, but there are other aspects of him that would still be relevant, such as his competitiveness with Naruto and his brother. I could also guarantee that he would be nicer to people, and would smile more. It's really not that hard to believe, believe it or not.
Change the history, and bits of the canon character's personality could also hold potential to change whether only one part of the history was changed, or you dump the canon characters into a modern day high school environment. That being said, while some change is inevitable in this case, it doesn't mean that the entire character has to change. Remember the taking notes tip? Consider which personality trait changes, and which trait is emphasized. I wouldn't cross out traits entirely, because even if the event that triggered Sasuke's thirst for revenge didn't happen, another traumatic event could still trigger it.
Romance and Love
I don't know which genre, or which emotion, gets more grief for characters acting "out of character" than this. Some people act like canon characters being in love gets an automatic stamp of OOC, especially if an OC as the canon's partner is involved. Yes, people can change when they like someone. People act different around different kinds of people for numerous reasons aside from being in love, so it's not as big of a stretch when a canon character has little changes around another character they like (whether this character is a canon character or an OC), but note that I said "little changes." After all, a truly violent character wouldn't change into a total sweetheart just because he or she liked someone. There would still be bouts of violent acts somehow, somewhere, to something, or even someone. I never said that the couple couldn't be an abusive kind of relationship, especially if one or both is canonically abusive.
Not every canon character is a romantic or would even know what being a romantic means, and not every canon character wants to be romanced and would rather things be more straightforward. Then again, there are canon characters who are romantic and want to be romanced. Use the quirks the canon character has to make the romance and the conflicts the pair faces unique.
As for characters whom are serial killers, I'm pretty much at a loss. Yes, a lot of serial killers have wives and husbands with kids, but do they really love them, or are they using them in order to pretend to be the average citizen? (Some female serial killers even kill their children for attention, or their husbands for money or material gain.) You could argue that they could, or at least they may want to love and feel love, but I highly doubt that the power of love will stop them from killing people forever and nor will the proof of love be able to convince a jury to forgive them just because he may never kill again. Getting out on parole is probably just as likely not to ever happen. Just look at Frank Breitkopf and Jane Hanratty from the show Criminal Minds as an example. However, in most real-life cases, male serial killers whom have girlfriends or wives, choose "damaged" women, or women with low self-esteem so that the man can make them feel whole and can manipulate them to stay in the relationship, or get them to believe their lies, no matter how outrageous it could be.
"Honey, what's that awful smell?"
"It's probably just a rat that died somewhere."
"Just one rat could make that big of a stink."
"Yeah, sure. It happened one time at my parents house. Boy, did it take a while to find it."
Then again, I'm not a criminologist of any sort, so I really wouldn't be much help in this circumstance.
Lastly, Don't Be Afraid
Don't be afraid to let the more serious characters act a little goofy, especially if they have acted as such in the canon material. Boy, did I not expect Kuroh from K Project to act like a little fanboy toward his late king, or that he would be a good cook. That was definitely a surprise. This also means that the goofy characters can also act seriously sometimes, or mellow characters can have extreme reactions to extreme events, or trivial events that are important to the character. People and characters are a spectrum, not just one thing for every circumstance.
Additionally, have confidence in your interpretation and in your writing, or, at the very least, don't put "he or she may be out of character." If you act confident, people will assume you are and that you know what you're doing, even if it's your first fan fiction. In other words, if, after all of this, you think your characterization is in character, then the readers will often agree with you for the most part. In any case, readers don't want to see that you think your writing may suck.