After the "Alabasta" Saga, no one had expected Robin to join the Straw Hats. Granted, she had helped Luffy and betrayed Crocodile, but it made her more of a wild card, and after the battle, she had disappeared. Then, just as the crew leaves Alabasta, Robin arrives from within their ship and Luffy, having rescued Robin from certain death, accepts her offer to join them. Added to that is that throughout the entire Baroque Works arc, Vivi had been played up as the potential next member of the Straw Hats, until she turned down the offer to stay behind and rebuild Alabasta right before Robin joined.
In the "Enies Lobby" arc, it turns out there was one more crew member to help out during the raid of Enies Lobby, and it's none other than...the Going Merry herself!
In the "Impel Down" arc, no one saw the return of the Broque Works agents, especially that Mr 2 would end up being Luffy's main ally in the arc.
This, admittedly, would have been much less surprising to those that read the manga rather than just watching the anime, as one of the chapter cover mini arcs (which by this point the Anime stopped adapting) featured Miss Goldenweek attempting to spring the members of Baroque Works from jail before they're sent off to Impel Down. All of the ones that ended up not escaping at the end of the mini arc (Mr. 1, 2, 3, and Mr. 0 aka Crocodile) appear in the Impel Down story arc when Luffy arrives there.
Dracule Mihawk shows in the "Jaya" arc for the Warlords meeting in Mariejois. Sengoku states that Mihawk is the one who rarely shows up during the meeting with the Warlords, Mihawk appearing because of news that actually interested him (Namely Zoro's first bounty).
Most people wrote Bellamy out as dead, and it's not hard to see why, seeing as his boss is Doflamingo and he went and pissed the guy off by losing to Luffy. Come the "Dressrosa" arc, not only is he still alive and still under Doflamingo's employment, he's also a participant in the tournament for the Mera Mera no Mi. Also, the appearance of Jesus Burgess was likewise something nobody could have seen coming. Later on, the supposedly long-deadSabo has shown up.
"Zou" arc: Stelly, Sabo's brat of a step-brother, shows up during the montage of royals preparing for Reverie, being a newly-crowned king.
"Whole Cake Island":
It was long-speculated that Sanji had at least two older siblings named Ichiji and Ninji, and some even guessed there might be a younger one named Yonji in the works. What nobody saw coming was an eldest sibling designated under the number zero and a sister to boot, because everyone was so used to seeing the male Vinsmoke side of the family in action via Sanji that the female side never really crossed their minds, and people are used to starting number counts at one. Oda pulled one directly from the Tite Kubohandbook in that it channeled the twist reveal Yammy was the number zero Espada. It should come as no surprise Reiju turned out to be a smash hit among fans merely due to the fact her existence was that much of a surprise to all when she debuted in the story.
As he was mentioned to have been defeated by Urouge and stripped of his rank of Sweet Commander, Snack was speculated to be dead or otherwise. It thus came as an unexpected surprise when he showed up.
A lot in the "Reverie" arc:
Moda the milkmaid from Ace's coverstory arc making a small cameo reappearance was very unexpected especially for this particular arc as she was a very minor character that only the most astute longtime fans of the series would recognize right away without being told.
People were surprised that Sai actually appeared at the Reverie since the Ruler of Kano stated Sai and the Happo Navy won't make it back in time for the Reverie after they left Dressrosa, and there was also a cover story of Sai and Baby 5's wedding at Kano. Naturally, people took his word for it since they doubted that Sai and the Happo Navy could make it to the Reverie in time.
Of all the people to make another appearance, very, very few guessed we'd ever see Saint Mjosgard again. Let alone that he'd make a Heel–Face Turn! Oh yeah and he's a Donquixote to boot.
The sudden return of Jewelery Bonney, last seen in a montage at the Dressossa arc, caught many fans off guard.
Nobody seemed to figure this arc would be where Bartholomew Kuma reappeared, most believing be would turn up at Vegapunk's lab to be repaired and upgraded. For him to return as a slave with swords stabbed into him and on all fours as a transport for the Celestial Dragons... such a sorrowful state is a heartbreaking sight.
After the Advanced Generation series ended, it was general consensus that Wallace, Gym Leader in Pokémon Ruby and Sapphire and Champion in Emerald, was another addition to the many game characters that got Adapted Out in the anime. To everyone's surprise, he shows up in the middle of the Diamond and Pearl series as part of Dawn's story, hosting a special Pokémon Coordinator tournament that bears his name.
Ash had Charizard rejoining his team, and not just for a big match like his previous returns, sticking around for the rest of the Best Wishes series. A couple of the other Pokémon Ash has captured could also qualify. For example, no one was expecting him to catch Muk, since in its debut, it actually received the least amount of focus out of all the Pokémon that appeared in that episode, only appearing briefly in a couple of scenes.
The Mewtwo from Genesect and the Legend Awakened is something of a double whammy — few were expecting Mewtwo to return, but no one was expecting it to be a different individual altogether, due to the backstory (and the logistics thereof) of the first one. To quite a lot of fans, this was far from a pleasant surprise as a result.
Clement's fourth Pokémon is Luxio — something no one saw coming. First off, it's a 'Mon from a generation not being actively promoted, and secondly, it's not even in the Kalos Dex (all three of them!).
Alain's full team reveal was also a case of this: his team is made up mostly of menacing- and tough-looking Pokemon like Tyranitar and Bisharp... and a Male Unfeazant. Similarly, May's rival Harley turns out to have, along with his team of sinister and threatening Pokemon, a Wigglytuff.
As one of the most popular Pokemon in the S/M, many assumed Ash would get a Rockruff. He did, but no one was expecting he'd get Kukui's Rockruff.
The last year of the Sun and Moon series finally broke the taboo against main characters capturing mythical Pokemon, with Meltan and Shaymin ending up on Ash and Mallow's teams respectively. Shaymin was particularly unexpected since the Gen IV Pokemon is not caught or promoted anywhere in the Alola games.
With Pokémon Journeys: The Series having a setup that involves visiting previous regions as well as the Galar region of Pokémon Sword and Shield, there was some hope that some characters from previous series would make an appearance, like Ash's previous companions. Even so, there were several surprises for the fanbase, like Gym Leaders and Elite Four members from previous regions, Team Galactic, and even Team Rocket members Butch and Cassidy, who hadn't appeared in the series for over a decade.
Pokémon Generations does this a couple of times, probably due to its format, but none of them can quite top the bombshell that appears at the end of episode 15—it takes place during the events of Pokémon Black 2 and White 2 and involves N's confrontation with his father, Ghetsis. Just when it looks like N is toast, an attack appears out of nowhere to save him. He then turns around to see Hilbert, the previous game's player character who had been Put on a Bus at the time of the second game's events. It's also this because most fanworks use Hilda, the female protagonist, as the main character yet Generations instead used Hilbert.
The series caught everyone off-guard with the first animated appearance of the G-Saviour, the Mobile Suit from a live-action movie that, for ages, many thought that Sunrise had went out of their way to ignore and even toss into Canon Discontinuity. The series throws in Mobile suits that viewers thought would never get animated, like the Superior Gundam and Blue Destiny units.
Gundam Exia Repair II got in the series due to 00's five year exclusive clause having expired TWO DAYS before this episode aired.
Gundam Build Fighters Try continues this trend with the Winning Gundam revealed to be a modified CAPG-78 Captain Gundam from the SD Command Chronicles series. And also, Domon Kasshu.
Another surprise comes in the Epilogue OVA, Island Wars, when are heroes are struggling against Scramble Gundam. So what do they do? They summon SUPERIOR FRIGGIN KAISER to counter it!
Continuing the Gundam examples, the manga MSV-R: The Return of Johnny Ridden features the return of yet another major character, namely Yazan "I'm Gonna Violate You" Gable.
Mobile Suit Gundam Katana, a Manga serialized in Magazine Gundam Ace from 2009-2013, was notable for featuring many designs that previously only appeared in Gundam video games. There are two noteworthy ones though that, while they're Variants rather than the true articles, the fact that their basis' received any utilization at all makes them count as this.
The MS-19 Dolmel was an Original Mobile Suit for Mobile Suit Gundam: EX Revue, a Fighting Game focussed on the original Mobile Suit Gundam series, serving as the Final Boss. It got an alternate variant here known as the MS-19 Dolmel Douhet. While it had two alternate variants before, they both went by non-indicative names like "Hawkeye' and "Katarl", whereas the Douhet makes it clear that its origin is the Dolmel.
The King of Dragon was a battleship from MSV90, a design series from all the way back in 1990. Of all things, they brought this back via an alternate variant known as the Kaiser of Dragons. What makes this special is that not only is it the first time it had any usage in over two decades, but its design (Being a mostly normal battleship with a dragon head at the very front) contrasts heavily with the design philosophy of the Universal Century, even in comparison to its more goofy-looking designs!
Gundam Ace Manga Mobile Suit Gundam F90: Fastest Formula brings back a couple of elements from the Video Game Mobile Suit Gundam F91: Formula Report 0122, with two notable examples. First is Bergh Scred, the Main Protagonist who hadn't seen any further utilization in the franchise at all up until this point. The other is Weibull Gardner, who actually had made an appearance outside of Formula Report 0122...once, in the 2006 Manga Mobile Suit Gundam Climax U.C.: The Bonds of the Bloodline.
Mobile Suit Gundam G40 was an Animated Short released on New Years Day of 2020, made to promote the HG 1/144 Gundam G40 (Industrial Design Ver.) figure and to celebrate the Gundam franchise's 40th anniversary. Since the trailers focused on reshoots of the first fight between Amuro and Char in the original series, most fans assumed that it would just be a reanimated version of that fight. What surprised fans though were a bunch of new elements implemented into the short to tell a similar yet different story. One of these elements is the inclusion of the mother of Amuro Ray, Kamaria Ray...as a starkly different character than she was before!For the sake of comparison... In the original series Kamaria was horrified that war made Amuro into a more violent person and cried over his transformation after he and the rest of White Base left, whereas here she has an ominous aura about her and it's heavily implied that she invented the Gundam in G40's universe.
In addition to Yugi and Kaiba you will be seeing a lot of familiar faces on-screen – characters previewed included Jonouchi, Honda, Anzu, and even Bakura.
Yu-Gi-Oh! ARC-V introducing alternate universe versions of Jack Atlas and Crow Hogan opened the floodgates of speculation on which other characters from past series would be brought back over the course of the show. The news that Kaito Tenjo from ZEXAL would be appearing in the Xyz Dimension arc was not entirely unexpected by the fandom, but the presences of Edo Phoenix and Asuka Tenjoin from GX certainly were, especially the latter due to their Out of Focus status in their home series.
Nobody would have expected to see Future Mai alive in Future Trunks' timeline, given that there was no foreshadowing of it within the series, and it was only spoiled by marketing.
Most of the Tournament of Power combatants for Universe 7 were pretty obvious, but a few of them had viewers scratching their heads:
Master Roshi had been Demoted to Extra ever since Z, and, power-wise, was the weakest of the Universe 7 fighters by a considerable margin. In the tournament proper, he ended up performing better than both Krillin and Tien, both of whom are much stronger than him.
Android 17 was a relatively minor character who had been Put on a Bus after the Cell saga and otherwise only got one role as the Arc Villain in a largely despised Dragon Ball GT mini-arc, so his return as a combatant came out of left-field for most. And even those expecting a return (Since he was memorable and largely well-liked outside of GT, and Word of God about what he did after the Cell saga made people interested in seeing him) were shocked by how much of a major player he was during the arc, going so far as to win the entire tournament and semi-inadvertently save all of existence in the process of doing so.
And then, after having to find a replacement for Majin Buu after he falls asleep, Goku ends up reviving Frieza, quite possibly the nastiest, cruelest, and vile character in the entire franchise, who also goes on to play a big part in Universe 7's victory.
Danganronpa 3 has Chiaki Nanami show up as one of the main characters, catching many off-guard, seeing as in the second gameshe was an AI who wasn't even hinted at being a real person.
It even manages to do this with a character from the same show, with the Side:Future character Chisa Yukizome showing up in Side:Despair as a teacher.
Charlotte's reappearance in Puella Magi Madoka Magica The Movie: Rebellion as Mami's pet/familiar was the last thing anyone expected. After all, she killed and ate Mami in the series and died shortly afterward. This was almost certainly a reference to the fandom's Crack Pairing of Mami and Charlotte, but it was still unexpected because no one thought the creators would incorporate something so bizarre into the official production.
HuGtto! Pretty Cure manages to one up both Maho Girls and Kira Kira. Everyone knew that Cures Black and White are going to appear in The Movie, since it also doubles as a Milestone Celebration. No one expected them to show up in the main narrative as plot-important characters. And over a dozen episodes later? Every Pretty Cure ever shows up, even movie-based ones, minor Cures...andBunbee.
A minor example, but while the first episode mentions in passing that Luluco's mom left, there was no real expectation that she was going to come back. Or be a badass, Stripperific, Space Pirate queen.
Despite SSSS.DYNɅZENON being a sequel to SSSS.GRIDMAN, there was initially little connecting the two shows together... that was, until Gridknight from the latter show appears out of nowhere in Episode 6, later joined by Anosillus the 2nd in Episode 7.
Tiger Mask W had multiple Legacy Characters, especially from Tiger's Den, but two caught everyone by surprise: Mr. Question due his sudden appearance at the GWM World Maskmen Championship (followed by crushing a Tiger's Den wrestler as befitting of someone bearing that name), and, in the last episode, Mr. No because...well, look at the original◊...
Magical Girl Lyrical Nanoha Reflection had five such characters. The first four being Arisa and Suzuka's parents (who, up until this point, had been Invisible Parents). The other is Shario, being the only post-A's character in the movie. And then chapter 6 of the manga featured a cameo of Misato Mikami (Nanoha's paternal aunt) who hadn't been seen since the Triangle Heart 3 OVA, 15 years prior.
Sailor Moon: Asanuma, a recurring character in the manga since the Black Moon arc, was seemingly Adapted Out of the whole series, so it was a bit of a surprise to have him briefly pop up in the final season.
In Deadpool: Samurai, Deadpool finds himself facing down Thanos himself and, in trying to find and bring in Captain Marvel via a special time/space device, accidentally initiates a crossover when he summons All Might. And this is canon to Marvel Comics!
JoJo's Bizarre Adventure: Golden Wind: As this part becomes very stand-alone from the other Parts when Jotaro and Koichi left the scene, seeing Polnareff from Stardust Crusaders returning much later on is unforeseen at least.
Grendizer U, a reimagining of the classic anime UFO Robo Grendizer, surprised fans when it was revealed that Sayaka Yumi, her father Professor Yumi and the iconic super robot Mazinger Z itself were set to appear, all of them Put on a Bus in the original series.
In addition to Yugi and Kaiba you will be seeing a lot of familiar faces on-screen – characters previewed included Jonouchi, Honda, Anzu, and even Bakura.
