In Chapter 77 of Hottie 3: The Best Fan Fic in the World, which involved fusion, all three Crystal Gems fused into one being. A few months later, the Steven Universe episode "Giant Woman" aired on TV and established that Gems have the ability to fuse with others. Even better, they all eventually did fuse together in a later episode.
Kara Zor-El and Dev-Em become lovers. Flash-forward several years and Dev-Em is one of her enemies in the main universe and the DCEU.
An alternate universe Saturn Girl is brunette, right like Supergirl (2015)'s Imra Ardeen.
Kara having a Legionnaire lover who wants her to move to the 31st century with him, several years before the Justice League Unlimited episode where Kara fell in love with Brainiac 5 and moved to the Legion of Super-Heroes future.
Satan Girl planning to force entire worlds to worship her like a goddess several years before Supergirl's Sterling Gates' run reimagined the character like a death and love alien goddess.
A Kryptonian doppelganger of a hero of the House of El plus Mordru plus the Legion of Super-Villains come together to destroy the Legion? And the Supergirl of Earth-One gets to do some fighting? It kind of sounds like Final Crisis: Legion of Three Worlds which came out nine years later, isn't it? Compounded by the fact Darkseid was the next Big Bad.
Kara isn't sure what she wants to join the League. A few years later, Supergirl would join the Justice League in the comics.
HERZ: In chapter 4 Asuka calls her daughter Akiko Aki-chan. Several years later, when Jimmy Wolk was writting The Second Tryhe named Shinji and Asuka's daughter "Aki-chan".
Avatar: The Last Airbender fanfic The Stalking Zuko Series has tension growing between the Northern and Southern Water Tribes, with North viewing the South as uneducated yokels and the South view the North as stuck-up busybodies who didn't lift a finger to help them when they facing genocide from the Fire Nation. Then Season 2 of The Legend of Korra comes out...
The GleeGender Flip story, A Different Direction, has Faith (female!Finn) complaining about Lebron James leaving the Cavaliers in 2010; a few months later, Lebron would return to Cleveland.
In Chapter 7 of Necessary To Win, Yukari infiltrates Anzio, which, instead of Saunders, is Oarai's first opponent. In the Anzio OVA, she ends up infiltrating Anzio as well, but unlike in the fic, doesn't get caught.
Tara Gilespie, author of the most infamous Harry Potter fanfic of all time, predicted in an author's note before Deathly Hallows came out that Harry would have to let himself die in order to defeat Voldemort, because he himself is a Horcrux. Fast forwards to when the book came out, and she was right! A lot of people had the same idea, to be fair, but the fact that Tara of all people figured it out is hilarious.
The Vampire DiariesGender Flip story, 'The Sara Diaries', features Stefan as a girl named Sara Salvatore. In Season Six, it was revealed that there actually was a Sarah Salvatore, Zach's long lost daughter.
Said story also predicted that Stefan and Damon's mother is still alive.
Weiss Reacts: The fic featured the Humongous MechaGurren Lagann as a regular plot element, had Jaune crossdressing for a Saber cosplay and Cinder joining the school as a teacher. Months later, the Atlesian Paladin is unveiled as a regular plot element of Volume 2, Jaune ends up crossdressing to cheer Pyrrha up, and Cinder ends up in Beacon as a student.
Similarly, plushies of Weiss are a Running Gag- and one Ensemble Dark Horse, Vivi, is an animated Weiss plushie. Now that Rooster Teeth have actually started selling Weiss plushies....
Back in 2001, an author named Kanius did Digimon Fusion (Digimon characters play the roles of DBZ) and is doing a remake called Digimon Fusion Kai around 2010. Comes 2013, that the english version of Digimon Xros Wars is titled 'Digimon Fusion'.
Somewhat an inversion of ascended fanon. The English dub version of Guilty Crown in the final episode's epilogue, the casts last words are "To the New Year!", then co-authors are doing a mega crossover fanfic based on New Years Eve.
Then plays straight in other parts. In Chapter 8, Captain Ginyu mentions his thanks of Freeza getting back his own body back. I wonder what happened officially in Dragon Ball Super?
Chapter 1 has Kirito mention himself being Samurai Jack, alongside the Minions of Set appears and Arago's super form looks like Aku. Then, Adult Swim renews the cartoon for 2016.
Chapter 32 shows the The Powerpuff Girls (2016 versions) siding with the Green Lanterns (John Stewart, Razer, and Aya). Promos of the PPG reboot shows the girls creating similar constructs.
In episode 32, a Spaniard Pretty Cure explains that there are other Pretty Cure teams around the world. A few years later, that would become canon.
The main character of this fan fic is named Chloe. As of 2015, Smile Pretty Cure! is being dubbed as Glitter Force, and one of the dub names revealed is Chloe (but the Chloe in question is Reika/Cure Beauty).
The first completed Naruto fic on FF.net was a Naruto/Sasuke fic (in fact, many early fics were). It ends with an author note that says "More Naruto fics, I think, are needed". Within six years Naruto would be one of the biggest manga fandoms and is only behind Harry Potter as the fandom with the most fanfics on the site.
Avatar: The Last Airbender/Mobile Suit Gundam WingFusion FicTears of Revelry was (by the author's admission towards the bottom) written prior to The Legend of Korra airing, and was first posted some months prior to Season 3. The prologue narrative briefly mentions that the Air Nomads "had regrown in strength" over a period of 150 years post-A:TLA, but not how. Then LoK Season 3 hit and it turns out that Harmonic Convergence caused a number of non-benders to become Airbenders...
Its version of "Ghost Godzilla" from All Monsters Attack was illustrated using a purple atomic breath. This ended up being the case in Shin Godzilla.
Early on in the story, Mothra Lea's changeling form is called a "rainbow changeling" as a joke descriptor because of how unlikely it seemed given the species is dark colored. Three years later in Season Six of the show and we ended up getting actual rainbow colored changelings.
The Bridge's King Sombra is an abnormal unicorn composed of dark magic, having a direct hoof in the "death" of Princess Amore, being able to hide in crystals; and coming back to life via dark magic and his surviving horn. IDW Comic's King Sombra released months later had all of these traits.
Red's Pikachu was shown using Thunder Punch as part of a way to make him stand out for Ash's Pikachu and other Pikachu in the series. In XY&Z, a Character of the Day named Jimmy used a Pikachu with Thunder Punch.
Due to not being announced at the time, the in universe Trainer Nations did not include Alola. This potential plothole was solved by the announcement of Alola having a system very different from gyms.
A silent Red with a Pikachu did eventually appear in the Anime, in Pokémon Generations anyway, a while after he appeared in Reset.
This fic predates Sun and Moon, where a Frontier Brain is able to use Mega Evolution.
A sarcastic Pokédex would later appear in Sun and Moon, albeit as a result of Rotom possession.
The fact that the final girl in the series harem (Anabel) was featured in the Alola games was completely unintentional, as the author mentions the chapter was in writing for long before that was revealed.
Reset's Chapter 26 mentioned Gladion when it went live in April 2017. A month later in May 2017, Gladion made his debut in the SM anime.
The Oak's Summer Camp Gaiden showed that Ash is a good baseball player like in some early materials by Shudo. Episode 28 of the Sun & Moon Anime showed Ash being quite passionate for a Pokémon variation of baseball.
Red is implied to be pretty built, considering he strongly resembles Ash, who is hinted to be noticeably muscular. A similarly buff Red would later show up in the Alola games.
Like in Reset (and the Games), Kiawe would obtain a Alolan Marowak. 2 of the moves used by the anime version are even the same: Shadow Bone and Flame Wheel.
After Misty obtained a Keystone in fic during the Battle Dome tournament, her anime counterpart would get one by the time of the SM Anime.
Kiawe's opponent removing their shirt mid battle occured in Reset's Kiawe Interlude a while before Brock would do the same thing. Even more: in a later episode, his opponent (a Buzzwole) engages in some muscle flexing, and Kiawe responds in the same fashion.
After a few mentions in the Resetverse of people trying to do more than a single Z-Move in a battle, Ultra Sun and Moon would allow the player to do so via the Rotomdex.
Also from the same game, the scene of Guzma engaging Team Rainbow Rocket Grunts follows Guzma's oneshot where he fought another evil team: Team Cipher.
In the Falkner Gaiden, Falkner acquires a Rainbow Wing to track Ho-Oh, and battles it at the top of a mountain. A few months later, Anime/PokémonIChooseYou would be released, in which Ash gets a Rainbow Wing which he uses to track Ho-Oh and fights it at the top of a mountain.
Professor Oak's friend, Doctor Boxer, invents a device capable of shrinking objects to store them in a small space. In the Sun & Moon anime Faba, of all people, invents a machine for that same purpose.
The Akala Island Adventures story's first chapter revealed that Frax and Velvet's shared Technique Bloodline is Tail Whip, as a reference to the few times Sun & Moon Ash helped out his Pokémon learning new techniques by wagging his behind. In the Pikachu Valley episode, Ash does actually get a fake tail to wag for a bit.
Pikachu uses a Quick Attack/Iron Tail combo to defeat Lilo's Mudsdale in the Fuchsia Tag Tournament. In SM 104, Pikachu uses the same combo against Hapu's Golurk, though unlike the previous case it doesn't work and he loses. For added hilarity, both Lilo's Mudsdale and Hapu's Golurk can use High Horsepower, which was a key move in the battle in Reset.
The first chapter of the Mewtwo Strikes Back adaptation was published exactly the same day the first proper trailer of said movie's CGI remake was released.
A biker briefly mentions "the Limeys" in the Kiawe Interlude. Years later, there'd be a Pokémon region based on England.
In the 2016 Holiday Special, Olympia has a prophetic vision involving a (symbolic) sword and shield. Lo and behold, Game Freak later went on to announce Pokémon Sword and Shield.
Ash's first battle with a Golisopod went about as well in both Reset and the anime: both Golisopod even managed to take a Z-move without any problem.
Trainer trading cards became a thing in Sword and Shield after having been mentioned a few times in Reset in passing.
The idea of there being gyms of all types was a thing in Reset long before Sword and Shield brought them in lore wise, with there being eight higher ranked (and thus the ones you battle) than the other ten.
Reset Misty's goal differs from her canon counterpart by focusing on wanting to catch one of every Water-type Pokémon in the world, something that involves her catching several Pokémon in incidental ways and with Professor Oak allowing her to keep her captures in his ranch. Years later, Ash's companion Goh from the Pokemon Journeys Anime ended up having a goal to catch every single Pokémon species in the world through very similar means, down to a Professor offering a place for him to hold his captures in.
Still from Journeys Anime, the Team Rocket trio ended up in possession of a black Pokédex with a very sarcastic and unhelpful behavior, very reminiscent of this story's Dexter.
The Cynthia Gaiden showed that Celestic Town was a dying, rundown town in Cynthia's youth, only regaining its prestige once she decided to become Champion of the region thinking it would help. In the Galar games, Marnie had the exact same idea, though it didn't work as well for her.
Lucario officially enters Ash's ownership after the Mewtwo arc. A few months later, a trailer for the Pokémon Journeys anime hinted that Ash would get a Riolu, which was eventually confirmed in episode 22.
Ash catches a Farfetch'd with a peculiar fighting style (wielding three leeks at once). In the Pokémon Journeys anime, Ash catches a Galarian Farfetch'd with a different battle style than the average Farfetch'd (via a larger leak and different typing).
Beforehis death, Jim Bader was going to make Ranma and Nabikis next child in A Very Scary Thought be an Expy of Erza, this time with Nabiki as the Fama and Ranma as the Ouma. When Erzas mother Irene Belserion is finally revealed, she is a voluptuous redhead who used to be known as the Dragon Empress. To be more specific, Ranmas ability comes from forming a pact with five Elemental Dragons.
A fancomic for The Loud House featured the Loud siblings, over the course of the comic, cosplaying as various different Nickelodeon cartoon stars (Lincoln as several male leads and Leni as Patrick Star for example) but the one that's this trope is Luna. Her cosplay is being stylized to look like Sam Manson, who turns out to share the name and gender of Luna's ultimate crush.
The training Ranma gave Vegeta in Human Saiyajin is pretty much the same training given to him by Whis is Dragon Ball Super. I.e showing him how to overcome the DBZ universes Unskilled, but Strong approach to martial arts by training him how to better control his ki and body.
In the House fanfic "I Am Not The Walrus" Chase inadvertently admits furries make him nervous, which House finds hilarious, sarcastically asking him if he was "ravaged by a herd of My Little Ponies". This was written before My Little Pony: Friendship Is Magic existed.
In the That's So Raven fanfic Support, Chelsea ends up pregnant by her abusive boyfriend and turns to her old friend Raven for support. Raven's Home later features an adult Chelsea and her child (a boy, not a girl like in Support) living together with Raven, and her twins, after Chelsea divorces her implied-abusive husband.
The first chapter, written prior to the release of the first issue of the Invader Zimcontinuation comic, features Dib almost getting into a dogfight with Zim with Tak's ship, only to realize that he doesn't know how to operate the ship's weapons, leading to Zim curb-stomping him. In Issue 2 of the comic, Dib is facing down Zim in a spaceship dogfight, and realizes he doesn't know how to use the weapons... and Zim tells him how, leading to Zim being curb-stomped.
Episode 4 of Season 1 has, as one of MIMI's hallucinations, a Shout-Out to The Shining in the form of a pair of meat children asking her to come play with them forever. This was published in 2015; flash-forward to 2017, and the comic series has a similar joke, wherein Dib (in GIR's body) imagines a bunch of copies of GIR asking him to come play forever.
Senior is a Communications Officer on the Massive who has no problem talking back to the Tallest rather than deferring completely to their orders. Then along comes the movie, which features the otherwise unnamed Comms Officer, who keeps trying to call out the Tallest on their Too Dumb to Live actions regarding the Florpus.
Episode 4 of Season 1 is loosely based on the unproduced episode "GIR's Big Day", which would later go on to be adapted as the first issue in the quarterly format that the comic series switched to in 2020.
In the first chapter of the first collection, Danny, Sam, and Tucker express their belief that E350 is going to fail to complete his self-imposed Halloween challenge (to do one chapter every day of October). Considering that (as of this writing) there's nine collections in the Halloween Unspectacular series so far, this comes off as extra hilarious.
One of the "Twenty Terrible Theories" in HU6 is that Rose Quartz was Pink Diamond, with E350 being exasperated by it. Two years later, this theory was confirmed by canon.
During the first book's Final Battle, Thor casually shows that he can still throw around lightning even without his hammer. Then along comes Thor: Ragnarok, and he has to go through a whole movie and an epiphany before he can figure out how to do that.
The first book's final battle also features Hulk smashing Chthon the same way he did to Loki, with the latter commenting on how gratifying it is to see it happen to someone else. Then Ragnarok comes along, and Hulk does that to Thor, with Loki being ecstatic about it.
Yet another from the same film is Thor's statement to Strange that "So Earth has... wizards now, huh?" Given that he used to be a wizard on Earth, that's definitely worth a chuckle from any viewer who's also a fan of this 'verse (though Strange's penchant for Trolling Thor and Loki is absolutely unchanged).
In Child of the Storm chapter 75, Strange tells Carol that her willpower is without equal, and she snarks that unless being really stubborn is going to make her bulletproof, she doesn't see how that'll help much. Guess which magical device he gives her? The Green Lantern ring, which works on willpower and can, in fact, deflect bullets (or do a lot of other stuff).
Seeing how Steve hooks up with Sharon Carter in the Marvel Cinematic Universe can be a bit awkward when you realize that she's his great-granddaughter in this fanfic.
Carol starts calling Harry "Luke Skywalker" in the finale of Child of the Storm for his kind and gentle nature, rags to riches story, Psychic Powers, and fighting skills. Pretty much the only thing missing is the lightsaber and the mechanical hand. Come Ghosts of the Past, he briefly gains a mechanical arm (albeit on the wrong side), and a glowing sword.
It's revealed in the final chapter of the first book - which came out before Doctor Strange (2016) was released - that Strange's ultimate goal is to guide the world into a timeline that results in the defeat of Thanos and that his time travel and manipulations are all to that end. And if that were not enough, in chapter 20 of the sequel, released in 2017, it's revealed that Strange is intimately connected to the Time Stone, which is closely tied into said plan to defeat Thanos, and his manipulation of people to that end. In other words, just like MCU Strange in Infinity War and Endgame. This did not go unnoticed, and the author was apparently deeply smug.
Repeatedly throughout the story, people react with disgust to finding out that Jon and Dany are in a relationship despite being related, until others point out that they're Targaryens, so that makes it okay. When this big Internal Reveal comes about in canon, no one other than Varys even acknowledges the incest aspect, and it's quickly brushed off when he brings it up.
Jon accepting the throne considering his adamant refusal in the show.
There is something darkly amusing about Jaime's angst over killing Cersei considering he died with his arms wrapped lovingly around her in the show.
Also amusing is that, in The Raven's Plan, Jaime killed the Mountain before killing Cersei, and the Hound went down fighting Euron, whereas in the show, it was Jaime who was killed by Euron and the Hound who killed the Mountain.
Bran's adamant acknowledgement that Jon is their King considering in the end of the TV series, he became the King of Westeros.
Edmure Tully is presented as having become much more dangerous and embittered after everything he went through. His final appearance in canon shows that even after everything, he's still as much an idiot and wimp as he ever was.
Yara and Theon's reunion sees her welcoming him back warmly, then kicking him in the balls to remind him what he's regained. In canon, their reunion when he rescues her from Euron involves her headbutting him before embracing him.
Ranma ½/Pokémon crossover "Fist of the Pikachu" has Ranma catch a Sandslash, and when he reaches Goldenrod City, his training causes it to evolve into a Steel-type new species. Its physical description is glaringly similar to Sandslash's Alolan form in Pokémon Sun and Moon, which also happens to be part Steel-type.
In X-Men 1970, Jean Grey leaves the Xavier's Mansion and looks for a teacher job. In the comics, the Xavier's Mansion became a real school one year later.
In early 00's fanfiction A Force of Four, Power Girl tells her father fitted her ship with a simulation because they didn't know enough about suspended animation... a technology which has played a role in every Kara's canonorigin written since.
Kara of Rokyn: During a scene, Superman's uncle mutters he'd look stupid in a pair of trunks, years before the "Trunks: Yay or Nay?" arguments among Superman fans.
X-Men: The Early Years: The next paragraph was written over one decade before Jean Grey encouraged Iceman to come out.
Bobby Drake was currently in the library, too, thinking and plotting. He owed Hank, and it was going to be the prank of a lifetime. He'd just finished a session with Professor Xavier, who'd explained that the reoccurring dream that Bobby had been having was "a classic fear of abandonment," and not what Hank had told him it symbolized. Now that he actually thought about it, how many ways could you interpret a dream of getting launched into space alone? Hank had told him it symbolized his wanting to explore new frontiers, and the rocket ship had represented a certain part of the male anatomy. He'd then suggested that maybe Bobby should go talk to Jean, because she could introduce him to some nice guys, and then his dream would go away.
In The Great Starship Battle, Chewbacca dies and is later resurrected. In 2014, the year after the story was written, the Star Wars Expanded Universe was rebranded as Star Wars Legends and declared to be non-canon. This meant that Chewbacca's death in the novel Vector Prime was essentially undone and he subsequently appeared alive and well in the Sequel Trilogy.
Starbound: Originally, chapter 6 was going to have an alternate opening scene involving Miyuki, after having finished a spinoff conversation with the twins from the others, spacing out and subconsciously focusing her gaze further and further on Mondo's butt as her tendency to space out combines with a high state of sexual arousal following him and Rokuna showing themselves off in some skimpy swimwear to everyone just a few days earlier. The author was told that not only would this still be Out of Character even with the setup, and that it not only does not equate with any of her previous blunders from the anime (which would result more from poor spatial awareness, hyper-immersion while reading, etc.) but said blunders are probably why she would be more careful not to act offensively, but that male and female sexuality do not even work the same way, with focus on anatomy being mostly a male thing. In a last-minute edit when Economy revised the entire chapter following his main beta-reader's return to business, Rokuna actually scoots behind Mondo to obscure her own body from Konata's view when she comments on how her Pimped-Out Dress could easily do with a Cleavage Window. Surely, that would've snapped Miyuki out of her gaze if she were to have gawked at Mondo in the first place.
The Dragon Ball Z fanfic "Atrocities" features Goku getting possessed and turning evil thanks to a wish from the Dragon Balls, and causing his energy to get colored black. It's also a crossover with a few other series including Buffy the Vampire Slayer and prominently features Spike. Over a decade and a half later, Spike's actorvoices a villain who uses the Super Dragon Balls to switch bodies with Goku with the evil Goku being called Goku Black, who appropriately has black energy. You have to wonder if Toei and/or Funimation knew about this.
The Second Anniversary Spectacularthon had a few teasing shots at a couple VAs. I mean, no way Vic Mignogna would've watched it, recommended by a few of his Rangers, right? Wrong. Thankfully, he took it well and the two have met a few times since.
Another one with LK and Vic — for their first Kamicon promo, Martin calls him Yuri Lowenthal. Vic voiced an Uchiha later in Shippuden.
Also, a good two years before the Abridged Series came out and made these types of jokes, the dub had a military captain in the Doma filler arc (who played the whole situation straight in the original) say that "as strange as it sounds, the fate of the world now depends on a card game."
Joey: Be careful, Yug. This guy means business. He wasn't even remotely intimidated by my Brooklyn Rage. Yami: Joey, stop trying to turn 'Brooklyn Rage' into a catchphrase. It's never going to work.
Episode 50 Joey Wheeler Ace Attorney had Joey up against the guy that banned the series twice already. The judge said that third time's the charm .. and a few weeks later, Little Kuriboh was temporarily suspended on YouTube for the third time.
Episode 25 featured a short sequence of Yami and Tea singing a duet, and the end stinger said 'that's the closest you're gonna get to yu-gi-oh: the abridged musical'. Several years and a lot of cover songs later...
From Episode 2, Chibodee Crocket, voiced by Takahata 101 using a Southern accent, tells a rambling story starting with the phrase "I ever tell you that story 'bout my best friend?" Later, Taka would play Ellis in Team Four Star's Left 4 Dead 2Let's Play.
In Episode 4, Taka voices the commisioner using the same voice he would later use for Dartz on Yugioh Abridged.
omg da new book iz kumming out rlly soon I kant wait!!!1111. I fink dat snap will be really the same person as Volximort koz dey are both haff-blood so dat will explain y he kild dumblydore and he hated hairy!!!!!1111 nd den hairy wil have 2 kommit suicide so voldimort will die koz he will rilly be a horcrox!!!!!111 omg I hope draco nd harry get 2getha dat will be so shmexxy, wont it?? If dey dont den JKR is hamophobic!!!!!111111 fangz 4 da help wiv facts, medusa u rok!!!111
A throw-away gag in 44WebVideo/Berserk Abridged 44 has two Strawman Political parodies arguing, which devolves into childish taunting, including the liberal one of the two calling the conservative parody a teabagger... this was made at the end of 2007, cue a certain political movement that appeared a year later.
The first line of the firstKirk/Spock fic is "Shut up. We're by no means setting a precedent." Of course, K/S went on to spawn Slash Fic as a genre, setting quite possibly the most important precedent in the history of fandom.
In the Final Fantasy VIII fic "Phantom Dreams", there's a joke about Zell's hair looking like a chocobo (and that's why Seifer called him a chicken) which was merely painfully unfunny until Final Fantasy XIII gave us a character with a chocobo living in his hair.
In 2004, a furry-based anthology comic featured a mini-comic involving a lupine boy band who turns out to be secretly gay behind the scenes. Obviously, it's meant to parody the rumors of homosexuality within real boy band members at the time, but with the coming out of Lance Bass and the outing of Ricky Martin (though many don't know he was a part of Menudo), you've got to wonder if the creator knew something we didn't. And, to make things even more hilarious, one of the band members in the comic is even named "Rickay"!
On 23 July 2010, a Power Rangers fanfic called "Mythic Rangers" was started, with one character named Hector. On 5 August, the names of the cast for the new 18th season of the franchise were leaked... the new green ranger is played by Hector David Jr. While the fanfic contains some deliberate Power Ranger references, this one was not intended.
A Final Fantasy XIII post-game fanfic written in June 2010 called New Dawn has Lightning, feeling empty and unfulfilled though happy her friends and family are doing well, go off on her own as if beckoned to go on another journey. Late that year, the Episode One novellas were released and the next month after, Final Fantasy XIII-2 is announced. What do they portray? Lightning, feeling empty and unfulfilled though happy her friends and family are doing well, go off on her own as if beckoned to go on another journey.
In the Katawa Shoujo fic "From Shizune's perspective," which was published before the full game was released, Shizune is surprised to find out that Emi is a lesbian, and Shizune says that "The track team captain being a lesbian is the sort of thing high school students would talk about," but that she gets left out of the loop because of her deafness. In Emi's route, while Emi is heterosexual, it turns out that the track team captain Hisao assumed was a romantic rival is gay, and Hisao appears to be the only one who knows of the captain and yet is unaware of his sexuality.
Speaking of Kung Fu Panda, the fanfic A Different Lesson happens to contain numerous plot points that come across as funny compared to plot points in later stages in the franchise.
When Tai Lung is attempting to 'lighten the mood' on the way to Chorh-Gom by helping Tigress and Shifu reconcile, Tigress has this to say: "And since when have you become an expert on entertainment and leisure? Did you take up clowning when I wasn't looking?" No...but at one point in the series, Ping practices clowning◊. (And now that that image is in your head, just try and keep from imagining Tai Lung doing and saying all the things the goose did when Tigress was sick.)
In Chapter 38, Tai Lung's thoughts: "No one needed to know he'd been so caught up in romancing Tigress he might not have noticed if Po had started dressing up in a cheongsam. Oh gods...why did I have to go there? Someone kill me now, please...or at least murder my imagination." Well, it may not be a cheongsam, but we have gotten to see Po dressed as a woman in "Ladies of the Shade". And Tai Lung's reaction is pretty appropriate.
On a related note, Song herself being a violet-eyed snow leopardess who is nominally on the side of the bad guys, performs a HeelFace Turn to help fight her former allies, and has a Ship Tease with Po sounds a lot like Jia.
The Big Bad is a dark master of chi who used to be allied with Master Oogway, but was eventually corrupted by his lust for power, leading Oogway to seal him away until he finally made his return centuries later, after Oogway's death. Are we talking about Heian Chao or Kai?
The third movie also has a moment where a panda dons Master Flying Rhino's armor (and which Po himself admitted to fantasizing about), and the statues of the Vault of Heroes appearing uncovered and open on the mountain around the stairs... And considering both Heian Chao and Kai are spirits, it's surely the case that Chao was also immune to the Wuxi Finger Hold, which makes Tai Lung warning Po not to use it incredibly prescient. It's a good thing the possibilities he suggested never happened with Kai, isn't it?
Tai Lung: Just what d'you suppose would happen if you used the ultimate chi move on the ultimate master of chi? The least that would happen is it blowing up in your face and doing absolutely nothing. Worse, you might just make him stronger...or allow him to turn it back on you, corrupt you, vaporize you...
Another more minor point of amusement: in the author's about me page, he notes that the voice he had in mind for Bao (Po's father in this fanfiction) was Bryan Cranston. Out comes Kung Fu Panda 3, and guess who Po's canon father is voiced by?
Rising of the Sleeping Soldier: When Alucard explains what he world was like to Ren, Itsuki and Motoyasu, Motoyasu thinks that Alucard's friends are his harem, only for Alucard to tell him that they are both men just to mess with him. This leads to Motoyasu thinking that he's gay. Both Word of Gay and Season 3 of the show confirms that Alucard's canon counterpart is bisexual.
Naruto and his friends learn to tree-walk and water-walk in the Academy, since the author thought it was a very useful skill, yet basic and easy enough to be taught in the Academy. Later, a Boruto episode that this is also the case in the Academy of the new era.
The Chunin Exam Finals has an even bigger example: Naruto, Sasuke and Gaara make it to the final round and are about to have a three-way fight, but Rasa protests and claims that the two Konoha Genin are going to double team his son. In the Boruto adaptation of the movie's Chunin Exams, Boruto (Naruto's son), Sarada (Sasuke's daughter) and Shinki (Gaara's adoptive son) make it to the final round, where they fight in a three-way match, and Boruto and Sarada, the Konoha Genin, end up double teaming Shinki, the Suna Genin.
Cat-Ra: Each season was written without the author having seen any further ahead, leading to some big misjudgements about where the show was going...or being quite prescient.
Catra Apologizes a Lot whenever she talks to Adora, when her HeelFace Turn on the show ended up being doing so for the first time in her life, to anyone.
Spinarella and Netossa are repeatedly described as "friends."
The physical effects of Adora's shadow powers are uncannily like Horde Prime's possession.
While acting like a cat from the First Ones' virus, Catra licks Glimmer's face. Later in the actual show, she licked Glimmer's arm.
In "Reunion" Bow's story about the academy has the extra complication of Catra supposedly being his girlfriend, to which Glimmer is quite put out that she couldn't have played the role. Catra even gives a further embellishment that Glimmer had a crush on him too.
Monokub himself points out that the false reality at the end of Season 3 bears quite a resemblance to his version of what happens in Catra's mind when she's infected with the First Ones' virus: waking up with no initial memory but quickly thinking the new reality is real, things disappearing with no one else noticing, and finally having to run from a destructive white force obliterating all in its path.
Two fanfics by writer TakaiTotem — Send Read Receipts and Peter Parker's Phone Calls — have a chapter or two each revolving around a waterfowl who only seems to exist to create chaos for the protagonists, doing things like stealing objects and delivering one-sided beatdowns to them (keep in mind that all of our main characters are superheroes). Sounds like a Shout-Out to Untitled Goose Game and the Memetic Badass reputation of its titular character...until you realize that the chapters he shows up in were written before the game was even announced.
Between My Brother And Me Mors Omnibus has Xavier (using a Fabled deck) fighting off against Yuzu and questioning why Fabled didn't have better support, particularly in the Spell and Trap department. The chapter was updated around the time the Blazing Vortex booster pack was revealed that has more Fabled support and both a dedicated Field Spell and Trap card for it.
Ultimate Sleepwalker: The New Dreams had multiple Take Thats aimed at John Kricfalusi, with one character in particular condemning him as a pretentious hack who constantly insults other animators' work while his own work is utter garbage. As of 2019, this view of Kricfalusi became widespread in real life, particularly after the universally-loathed Cans Without Labels was finally released six years after its due date.
The author notes that Danganronpa Another Episode: Ultra Despair Girls also happens to have a character named Masaru, and learned of Masaru Daimon's name after giving her Masaru his name. The fic started in May 2014, and DRAE came out in September of that year.
This fic has an Ultimate Assassin who turns out to be one of the good guys. In New Danganronpa V3, it's revealed in the midgame Maki's true identity is the Ultimate Assassin, and she's one of the good guys. Even better yet, Shuuya nearly kills Saemi in revenge for Miyako's Heroic Suicide (and kills her during her execution to prevent her from going out on her own terms). Maki tries to kill Kokichi (the supposed mastermind at the time) after he abducts Kaito, and later offers to kill the real mastermind, Tsumugi.