So, you're here because you want to learn. You're not a good enough writer to write within the Kingdom Hearts universe, you're just lazy and don't want to make up your own characters. No problem! This absolutely non-satirical guide will help you be Great Alterante Universe Writer #250394762. Let's start with the basics. The easiest cliche is a boarding school. So let's hit that first!
First of all, we all know it's some kind of boarding school. So let's neglect to write ANY classroom scenes. Those are dumb and serve only to further what all the losers that think they can write call a "plot." It also takes too much energy to write something without gratuitous amounts of romance and making out. It's not really a boarding school, so much as a big hotel with classes nobody goes to. You can, of course, write hallway scenes, pretending they actually went to their lessons. But they're just too cool for that. Look at Roxas. No one with a ska wristband would go to a boarding school class (sober at least). He'd be too busy rocking out to the Planet Smashers. Then again, the Planet Smashers rule.
Next - it has to be sloppy, hot, teenage romance. Now you can write het and yuri but that's just not hip. Nobody's gonna read that. This fanfiction community is filled with psychotic fangirls who will read anything if it involves two feminine boys manhandling eachother. Yes, even Tron/Goofy. So, feel free to remove every girl from the story. No sexual discrimination here - just the fact that you can't have hot gay sex with girls around to try and claim your HOT BISHIES for their own.
AU means that you can take people incredibly out of character. Ignore the blatant homophobia they would be expressing at this age (like teenagers do, you'll learn when you're older) and pair them up willy-nilly. For example, you can suddenly make Roxas exist again - it's your fanfic! - and have him be Sora's long-lost... person of just enough distance in relation so that they can get it on in their bedroom. No sex, of course. Just incredible uncharted levels of innuendo and suggestive themes. Then they have to be interrupted by Other Gay Couple #95786912433496684 before the hot stuff starts going down because that always happens in real life.
Of course, as I've said, since original characters are the SPAWN OF SATAN and should NEVER be used in ANY circumstances lest we have a bunch of MARY SUES about (listen, we could have well-rounded fan-made characters but that's far too big a risk to take), we just have to mess up the characters ourselves. So we can take chipper, eager Sora and turn him into gothic-punk-khuul-kid boy (khuul is a morrowind reference, it's the name of a very little port/fishing town on the northwest portion of vvardenfell.) that is apathetic. Also, he has NONE of his interest in Kairi. She's out in some yuri fic right now. Can't be bothered. Besides, SoraRikku is canon. So canon, the game developers decided they shouldn't put any evidence of them in there.
Speaking of canon, it's all a load of garbage and we can ignore it. AU, remember! The Organization, Heartless, and our heroes are all best friends 4ever (they even have BFF rings, thank you) and WILL show it to the whole wide world gladly. YOUR world.
And throw out those nasty Disney characters, too. No, seriously, I mean it. They're obnoxious, besides maybe the tron guys. And they're not HOT BISHIES so that just rips them out of the picture. Then again I'm sure some of you played this and promptly declared "wow mickey kicks ass o.o" but like I said, they're missing the hot factor. And people just don't like them. Nevermind that the game pretty much revolved around them. Maybe you can keep Mushu, though, because he's really cool and is a tiny little dragon. I always liked Mushu. You should all like him too.
And there you go! You've started on your way to having your very own great AU fanfic! The reviews will be coming so fast that they will take solid form and eject from your CD-ROM drive and printer and give you thousands of little papercuts and flood your entire house with little pieces of paper saying "write mor i luv dis" or "OMG NOWAY SORARIKU SORAROXAS", maybe even a "I WAS PROMISED TRON/GOOFY" for good measure. Congratulations, Great Alterante Universe Writer #250394762. You are a God amongst a large, loosely-knit community of Kingdom Hearts fanatics.
Now I gotta go. I have one of those "wild party" things with my "friends" and we're all going to play "Guitar Hero" and pass out on the "floor" within 30 "minutes."
Because Guitar Hero is fun.