DOs and DON'Ts of a Fallout fanfiction

The way you talk? Talk to me like that.

There's this age-old issue fanfiction authors have: how to avoid a character accidentally being OOC?

Well, I've got a very simple answer for you:
Listen carefully to the way they speak.

Like 80% of how a character is perceived by readers is how they talk. There's this thing called idiolect - individual dialect, every single person has it. It's the way you speak, and it's unique for every single human being! And that's basically what you're looking for in the characters.

If you ace the dialogue, it won't really matter how the character acts (unless they do something completely off the hat) and your readers won't complain about them being OOC. That's why dialogue is so important.

You need to know exactly how that person talks.

Paladin Danse will speak more formally, even in the case of casual conversations. He will be more likely to use correct grammar, as well as utilize more expansive vocabulary. The usage of military slang is to be expected as well, so you might want to brush up on that too. See what I did there? Just read it in his voice.

Take, say, MacCready. Um... The Fo3 MacCready, I mean. That's a completely different story. Don't be afraid to abuse the word mungo, he will say that. And swearing. That kid swears like a sailor. And his face looks like your butt. He's immature and mature and the same time. He will get irritated easily, especially when he thinks someone is stupid. Which he thinks about everyone.

Again, the best cure is playing the games a lot. The characters will just sort of brush on you and their way of speaking will just because natural.

I'm not saying you have to be 100% correct, but be careful not to be 100% wrong, too.

The Brotherhood of Steel, for example, is by nature a more formal and organized structure, so I don't care if you're writing about Elder Maxson, Sentinel Lyons, Paladin Danse, Scribe Haylen, Star Paladin Cross or whoever else, keep in mind that they won't likely come up to you and say "Hi! How've you been?" That... doesn't click. So look out for stupid mistakes like that.

Now, I know idiolect isn't just about vocabulary, but also grammar. Everyone just speaks in their own way, and that's fine. Still, you should know how to recognize various characters' idiolects.

Let's say that you're about to do something stupid and your companion doesn't agree with that.

"Just don't say I didn't warn you." That could very well be Deacon or Hancock.

"I don't think that's the best thing to do..." Add a "Blue" and you get Piper.

"This is likely to be dangerous." Either X6-88 or Star Paladin Cross.

"I don't think this is the best course of action." That's Paladin Danse.

"Whatever you want, just don't come crying to me after you get hurt." Depending on the tone, something like this could be said by MacCready, Butch, or even Nick Valentine.

Idiolect is also an amazing way to show who the character is without naming them or describing thoroughly. Great thing to use if the reader's supposed to recognize them before the main character does.

For example, my OC, Carley, is sitting in a bar. She's a trader up from Quincy and hasn't been in the Commonwealth for very long. Someone enters the bar, but she doesn't look at them, focused on her drink. The newcomer asks "Do you sell any non-alcoholic beverages?", and that's when you guys already know that's Danse, even though Carley hasn't looked at him yet. If the person says "Just water would be nice. Thanks big time." in a feminine voice, it'd be safe to assume that's Piper. Know what I mean?

So yeah, that's basically it.

Word for today: idiolect.
Don't know if you had known about its existence before reading this, but it's a hella important thing.

(And knowing how to operate on several different idiolects is the basis of being a fanfiction writer, so get to it.)