Recursive Fanfiction

Fan Fiction is a popular medium, and thanks to the nature of Sturgeon's Law, some of it can indeed be quite good to read.

And some of it may actually become so "interesting" by said readers, that they are inspired to want to make "fanfics" based on the writer's story, despite the fact (or perhaps, because of it, in some cases) that said story is fanfiction in and of itself...

This is Recursive Fanfiction.

Care should be taken with this trope, as the story that said fanfic is based on must be a fanfiction as well. If the fiction that it is based on is not itself based on another work of fiction (or fanfiction, which would make the fanfiction of said fanfic fall under this trope as well), then that's a normal Fanfic, and not this trope.

Or, schematically:

Original fiction -> regular fanfiction -> Recursive Fanfiction -> still Recursive Fanfiction, but of a higher level.

Not to be confused with Meta Fic.

General/Crossovers

 * MSTings in general.
 * Project Horizons by Somber—a Recursive Fanfiction for the My Little Pony: Friendship Is Magic/Fallout crossover fanfiction Fallout Equestria by Kkat—has already spawned fanfiction of its own.
 * Drunkard's Walk has inspired a number of fanfics, collectively known as The Drunkard's Stagger, as well as an author-recognized sequel to Drunkard's Walk II.
 * Turnabout Storm got Turnabout Storm: The Other Side as an unofficial parallel story where Phoenix Wright's Friendly Rival Miles Edgeworth and Professor Layton get involved in the crime's investigation.
 * Dungeon Keeper Ami has spawned several of these (though most of them are short one-shots).
 * The Secret Return of Alex Mack spawned so many fics by other authors that it became a Shared World, The Teraverse -- and so did the greater setting of which it's part, A Brane of Extraordinary Women.

Anime and Manga

 * Nobody Dies has several sidestories written by both the author and others, including Six AIs, One Continent and The Kei Files.
 * Kyon: Big Damn Hero has Traveller.
 * Neon Genesis Evangelion: R has Evangelion: Redemption.
 * The Death Note fandom has at least two fanfics that inspire recursive fanfiction:
 * Poison Apple by Robin Rocks and Narroch has five: Human, Doom, My love, The End and Broken Fairytale.
 * PITCH by uberneko-zero has two: A Different Shade of Pitch and Lips.
 * True Elision very recently inspired a Kink Meme fill: The End which in turn got its own sequel Heart. Ironically, the first two are yaoi and the last one is Het.
 * The Finale of the Ultimate Meta Mega Crossover technically counts, since it contains references to at least three different fanfics ("Thousand Shinji", "Shinji and Warhammer 40,000", and "Once More With Feeling"). However, it's more notable for being infinitely self recursive.
 * Shadow League is a fanfic based off the infamous Dark Fic Pokémon Master, amongst countless others.
 * Say what you will about the infamous Axis Powers Hetalia "Economic Crisis Gangbang" Kink Meme fill and its content, but it proved popular enough to spawn a plethora of spinoffs about America's PTSD after the event, what would have happened if the other nations had mistaken Canada for America or if America had actually put his Super Strength to good use or chewed out the other nations for their heartlessness, a consensual or at least less disturbing version of it, etc.
 * The Tear Jerker ending of the US/UK doujin Silencer affected some readers enough to write/draw Fix Fic for it.
 * The infamous Gorn fic Debt has a recursive parody fanfic written by its own authors, in which the first chapter is rewritten as a cosplay game Gone Horribly Wrong in which the China cosplayer turns out to be a psychopath and breaks out the knives. Taking this as an implication that the writers wouldn't mind it being parodied (particularly since they expressed pride that the original Debt nearly ended up on the So Bad It's Horrible page), someone made a fanart piece depicting China confronting his Villain Sue replacement (not work safe for swearing, blood, and suggested extreme violence).
 * In Flight has spawned several spin-offs, most notably The Emiya Clan.

Film

 * The Private Diary of Elizabeth Quatermain apparently has several.
 * The Lost in Time Series has one called Lost in Time: Destiny.
 * The well-known How to Train Your Dragon fanfiction Hitchups got one, a oneshot based off the story with the author's permission called The Elder's Prediction.

Music

 * There are multiple fanfics based around Act 1 and The father of Death by The Protomen. Which themselves are a set of two Dark Alternate Universe Fics based on the original Mega Man game.

Literature

 * Harry Potter and the Methods of Rationality has not only inspired its own fanfics, such as Once Upon a Tower and Nightmares of Azkaban, but "Rational" fics have become a kind of sub-genre.
 * The most famous Rational fic beside Methods, Luminosity, has spawned several fan short stories.
 * The large Harry Potter projects The Shoebox Project, Dumbledore's Army and the Year of Darkness and the Dangerverse have their own fanfic.
 * All the sequels to My Immortal.
 * The Hogwarts Exposed series is the rare example where it is based on both a fanfiction AND canon, so it is filled with plotholes. To be more specific, the author based it on The Psychic Serpent series as his canon, and the defeat of Voldemort as it is described in the intro of the first fic, is based on Mists of Time by Nightfall. All of these fanfictions, including The Draco Trilogy, were written during the 3 Summer period, where HP-fans had to wait 3 years till book 5 was released, and Hogwarts Exposed was written during the end of that period. But starting with the second fic, Hogwarts Too Exposed, the author started retconning things from the new canon into it, while simultaneously still clinging to The Psychic Serpent. One of the biggest plotholes is this: At the beginning of the first fic, Hogwarts Exposed, Harry explains to Hermione why he left the Wizard World, and left his Wand at Sirius´ place, and Sirius is at the end of the same fic invited to Harry and Hermione's wedding. But in the third fic, Hogwarts Overexposed, it is mentioned that Sirius was killed by Bellatrix, just like in canon. None of this is ever explained.

Live-Action TV

 * There are quite a few stories written by authors other than the original CP Coulter that use original characters from the Glee fanfic Dalton.
 * The Harmon Verse, a series of Glee fanfics centred around the Original Character of Jack Harmon. It includes four ongoing novelizations of Glee and over 40 stories altogether.
 * The Contract has ended up spawning a number of other fanfics, forming a world known as the Contractverse. They include:
 * Lifeline, a companion piece to The Contract.
 * Exigencies, a Continuation Fic for The Contract.
 * Recovery, Where the Rails Converge, and A Gentle Knock at the Door, all separate sequels to Exigencies.
 * PATIENT, a sequel to A Gentle Knock At The Door.
 * Creepy Pencil Story, a short "What-If" story,
 * Pencils are Dangerous, a sequel series to Creepy Pencil Story.
 * The Kindness of Strangers, a oneshot addition to Pencils are Dangerous.

Video Games

 * There's been at least one doujin based on Patch Con, itself a Touhou fangame.
 * People seems to like the concept of Advent Cirno a lot, and there are a lot of fanarts of it in Pixiv.
 * Poke Wars has spawned three fics written by Jakayrta set in the same universe. Two of them became canon.
 * Another Pokémon example: there have been multiple fanfics written based on Black Adventures.
 * The Portal fandom is involved in a rather complex graph of Recursive Fanfiction. From top to bottom:
 * Homestuck; Portal; Team Fortress 2
 * Portal mods
 * Portal: The 4th Millennium; ITS MY LIFE! & TEEN FORTRESS 2
 * The Inevitable Sunset: An Impossible Continuation; Skepkitty's MSTs; MarissaxChell & Portla 3 (Lost Forever)
 * HIT THE BERSERK BUTTON! MSTs
 * And that's only counting 2011. 2012 brought us fictional Horrible Fanfictions and Portal: The 4th Millennium: The Troll Fic Edition.
 * Kynrind's Capture is one based on the Porn with Plot Warcraft fic, Ethereum Gladiator.
 * Subverted with Morphic, where a new author was supposedly going to write his own sequel to the original fic... only it turns out the whole thing was planned out ahead of time by the original author as part of an elaborate April Fool's prank.
 * Undertale fandom, due to their love of creating AUs and intercrossing them, is excessively prone to it. Not helped at all by that two of the most popular AU, Underswap and Underfell are technically ownerless so many people does their take on them.
 * The famous Fan Web Comic Handplates has generated a lot of fanworks. Things got worse when its author, Zarla, released a desktop companion based in the version of Gaster she uses in her comic, which on turn has also generated an interesting amount of fanart by itself.
 * Due to constant crosspolinization of AUs, every AU crossover is technically this. Very memorables are X-Tale (where a deranged Sans from an universe that got destroyed goes from 'verse on 'verse destroying them in a effort to restore his own), and the "Bad Time Trio" fancanon (where Canon!Sans finds himself trapped with the characters that take his plot position in other two AUs, Papyrus from Underswap and Chara from Storyshift).

Web Comics

 * Homestuck out the wastechute. Fans will create Alternate Universes, the alternate universes will become popular, people will write fanfics set in the alternative universes... and then there's the fanart of alternative universes.
 * The Grand Battle is the most notorious in having fanart and other fan stuff based on itself.

Web Original

 * There is a whole community of people writing fanfiction based on Yu-Gi-Oh!: The Abridged Series.

Western Animation

 * My Little Pony: Friendship Is Magic has several fanfics that have been fanfic'd. Some of them:
 * There's the My Little Pony: Friendship Is Magic fanfic The Conversion Bureau, which has spawned tons of fics set in the same setting or a variant thereof; no wonder, since it is a very convenient setting for Wish Fulfillment and satisfying one's desire to live in the story. Its misanthropic tone has, however, spawned responses like The Conversion Bureau: Not Alone.
 * Fallout Equestria has a number of sub-fics. And by "a number of sub-fics", we mean over 200 of them. The most notable is Project Horizons, which has even spawned fanfic of its own.
 * Cupcakes has several alternate ending fanfics written, and a few sequels.
 * Rainbow Leap is a Quantum Leap-inspired ponyfic wherein Rainbow Dash basically tries to fly faster than ever with some Applied Phlebotinum from Twilight Sparkle - and ends up dimension travelling through not only Cupcakes but several of the fanfics based on it, making it a recursive recursive fanfic.
 * Progress, focused on Princess Luna adjusting to the changes in Equestrian society over the last thousand years, has inspired Luna Vs. Videogames, Celestia vs. Time, and the NSFW Luna Vs. Threesome.
 * Luna having an abacus is mentioned in several otherwise unrelated fics.
 * Better Living Through Science and Ponies spawned a Chapter 4.5.
 * Silent Ponyville Chronicles has gone on to spawn at least three different fanon continuities, some of which have had a significant influence on the central continuity. Also has a DeviantART group with plenty of fanon works.
 * The Pony POV Series is relatively new, but has already spawned another Discorded Ponies Series fanfic and The Letters To Ponies series.
 * Also, the fangame Story of the Blanks is referenced as a real occurence in a lot of fanfiction.
 * The Daria fanfic God Save The Esteem has spawned a prequel, Moving Pictures, as well as numerous other stories up to and including the obligatory lesbian Slash Fic.
 * They both started being written at around the same time, so it's more likely that it's two different, but similar series that ended up sharing their continuity.
 * The Kim Possible fanfic A Small Possibility, with the author's given permission, has spawned many a Kim/Shego fanfic featuring their spawn from the original, Kasy Ann and Sheki Go.
 * The fanfic Strays, hosted in the Young Justice Kink Meme, has several future-fics set to it and attached its thread despite the story still being in its early stages and in the process of being fleshed out. There is also fanart for it, featuring the costume designs for the Batkids' new hero identities.