**This is supposed to be broken up into paragraphs, but the site is ignoring my attempts to do so** I tried posting this as a private request last night, but then thought it might be more suited for this format. The way it works is by drawing a few unconnected plot mechanics from different series and putting a twist on them to make something more interesting.
The first concept is 'Mantling', which is essentially to live another being's life so thoroughly you become them. The concept (at least as far as I am aware of it) originally comes from the Elder Scrolls game series and mostly, if not always, involved divine characters. In this case it could involve characters with or without power.
In this case certain rather obsessive members of fandom/nerd culture, however you want to put it. Discovered, that with enough dedication you could become one of these characters. Bodies would change, memories would be received, potentially power if the character in question was not from a more realistic setting. Even drastic changes were possible like becoming a character of the opposite gender or gaining a body that was not human.
Ultimately the process is better described as fusion to a degree. Physically you become a perfect match for the character and gain their memories and personality to a large extent, but you don't forget who you were either.
This is where the 'masquerade' becomes part of the story (inspired by the same idea in the 'World of Darkness' game system, something I am only familiar with but familiar enough to like the idea). As the number of these individuals slowly began to grow, it was quickly understood it benefited everyone to keep a low profile. Whether you had power or not, it became important to hide what you became and to keep this a secret as much as possible.
Behind the scenes there was a coup of sorts, some of the most powerful individuals blackmailed, bribed, seduced, intimidated (and occasionally just got rid of) enough people in power to make things slightly easier, to make it possible to alter documents and official identities and prevent people from digging to deeply. A small number of outsiders now know but have learned to keep quiet about it, and the masses have no idea. And the people who have gone though the process are bound by strict rules to conceal their identities and sometimes powers, with a little more freedom in specific situations where there are only people like them around and little chance of outsiders seeing anything. Those who break the rules can be punished severely, though how severe depends on the details.
The idea here is to play two or more characters involved in these circumstances (with the characters they change into being either anime or video game sourced). Maybe they are newly changed or in the process of changing, or perhaps they have been for some time. Preferably with relationships involved, I could play male or female characters (who may or may not have changed genders in the process), MxF or FxF or MxM couples are all allowed (though I personally don't write MxM). The idea is a mix of fairly frequent sexual and non-sexual content. It could be a mix of light and dark content.