I really like the idea of your setting. I only have the sourcebooks for D&D, but I still want to be able to help even if it's simply giving out ideas that might be able to be fully statted by someone else.
Balance of Power
From what I believe, there would probably be some kind of balance of power between the Pre-Vanishing reals, the Post-Vanishing reals, and the fictions.
The Pre-Vanishing reals remember the time when the lives of fictions were completely up to reals. They remember when a single button press, die roll, or keystroke would alter the lives of a fiction, and they are the ones most likely to regain that control. However, they are not used to living in a world with so much magic and technology.
The Post-Vanishing reals see the magic and new technology as being normal. They find themselves using it more easily than the Pre-Vanishing reals, but they're mastery of magic and technology still doesn't match that of the fictions who originated from magical and/or technological universes.
The fictions themselves come close to having demigod like power. They usually either have amazing abilities, are able to use magic better than any real, or are able to use technology better than any real. But some of them have realized that there was a time when their individual creators had complete control over their lives. Some of them are still controlled by the methods their creators had used.
If that would be an accurate set of descriptions of the three groups, then it would form a kind of rock-paper-scissors relationship where pre-vanishing beats fiction, fiction beats post-vanishing, and post-vanishing beats pre-vanishing.
Controlling Fictions
Fictions can be controlled in a variety of ways. But a fiction's creator gets a bonus to all attempts to control their fiction.
Video game fictions (or all fictions if you wish) would be able to be controlled by controllers. The commands that could be limited by the controller. Controllers with many buttons (N64 controllers) would allow more things to be done than simpler controllers (Atari controller). Using a controller should require a skill check with the more complicated controllers having a higher DC to use. Also, the fiction's dexterity modifier is replaced by that of the person controlling him/her. Fictions can resist the control with a successful will save, but the controller will automatically lose control over the fiction durring climatic moments, while having a conversation (but the controller can still influence their answers to "yes" or "no" questions), and while listening to a monologue. The fiction's automatic regaining of control is usually known as a "cutscene".
Another way of controlling fictions would be through the use of a specially prepared sheet known as a "fiction sheet". A pre-vanishing person trained in its use can create one and make changes to it that would affect the fiction for a limited period of time. The "fiction sheet" would basically function like a voodoo doll. The fiction in question can make a will save to resist the changes. If they fail the will save, they must then make a fortitude save to avoid taking damage from the sudden change to themself. Small changes (a single point added to a skill rank) would have higher will saves to resist, but lower fortitude saves, while big changes would have lower will saves and higher fortitude saves. The bigger the change, the greater the damage that would be done for failing the fortitude save.
Another way of controlling a fiction would be through the use of a fanfic. Fan-fics control a fiction by deciding what they'll do when a triggering event happens. The triggering condition would follow the same rules as the one for the programmed illusion spell. When the fanfic's triggering condition is met, the fictions involved each make a will save with bonuses if it would be out of character for them to do follow the fanfic's stated course of action. If any of the fictions involved succeed in the will save, the fanfic's effect is ruined. The fiction gets another saving throw everytime the fanfic trys to make them do something out of character and everytime a real intervenes in a way that goes against the fanfic (almost anything that the fanfic doesn't mention). The fanfics would basically function something like Unkei's (from s-CRY-ed) Mad Script ability.
Special Controllers
Light Gun and screen: This controller allows the user to control a target fiction's ranged attacks. The target fiction must have a ranged weapon for this controller to affect them. The target fiction loses the ability to attack on their own, but still retains all other control of their body. Their attacks are instead performed by the controller's user on the user's turn. The attacks are made with the user's ranged attack bonus, but otherwise act as though the controlled had made the attacks. The user may also reload the controlled's ranged weapon as a move action whether or not the controlled has any ammo for it (just point the gun away from the screen and fire). The user is also able to see what the controlled sees through the screen.
Other Ideas of Mine
1. Coastlines becoming a battleground for a war between pirates and ninjas.
2. Rent-a-Zilla... I don't think I have to say much more about that.
3. Some kind of variant Monster Trainer class where the monster is a video game fiction. It would be available to Pre-Vanishing Humans.
4. L337 could be a language that could be learned and even spoken in.
5. What if some characters/groups that would normally be made as fictions were made as reals instead? Just imagine a Coreline where the MIB had secretly existed even before the 23 hours. What if a videogame and hotrod-loving, overweight real named "Coop" managed to salvage a giant robot that had appeared durring the 23 hours?
6. What if Jack Thompson lived in Coreline as a pre-vanishing human? How would he react to characters from various violent games he's tried to ban becoming flesh and blood? How would those characters deal with him? Jack Thompson would be very likely to join the AOH. Heck, he could be the mastermind behind the KOTT.
7. What happens when another Earth in another universe experiences the same thing that Coreline did and pulls people from the original Coreline as fictions? What happens when a member of AOH has been placed in another dimension where they are a fiction? How do we know that the universe that Coreline exists in is the first to experience such a thing? The universe that Coreline exists in could turn out to be just as real as the ones that the fictions came from.