Basically, I am assuming and am predicting cases where recognizable or otherwise characters, like this one, without any copyrights are put into a copyright, for instance said character fucking a Pokémon. The Pokemon in question is not a fan_character, but neither would be the character.
So, I am thinking of a tag for these instances that would function like fan character, but inversed: the character put into a copyrighted world, instead of a character made in a copyrighted world.
I initially thought of self_insert, since it exists, but I immediately thought of the literal term: the author, a real life person, inserting themselves into their literature. But, this would both be TWYK and hard to tag, the only example I can give is Andrew Hussie quite literally inserting himself into his webcomic, Homestuck, as an official character (that, and it would be easier to rationalize using your fursona instead of you). I then thought up of character_insert, where a non-copyrighted character is put into a copyrighted world, be it a game, webcomic, book, or maybe even art if you want to go that far. This is not to discard self insert, it can still be used with source information.
In summary: should we recognize/use a tag called character_insert, where characters that do not have copyrights behind them are put into a copyrighted setting.
Here are some examples (updating):
post #1117034 post #1079096 post #1055555
post #1027708 post #1025981 post #995663
Updated