Cryptic Background Reference / Anime & Manga

• Considering Blame! is a series that prides itself in its sheer vagueness, it isn't a big surprise that this trope shows up at least once a chapter. Technology and factions are seen, mentioned and interacted with often, but in most cases, never fully explained. This adds to the already frighteningly vast feel of the 'Verse, and leaves plenty of room for Wild Mass Guessing.
• Cowboy Bebop does this all the time, sometimes without even directly saying anything. It oftentimes does this with the main plot and character traits — e.g. Ein is a "data dog", something apparently important and rare which is only vaguely explained, even in the episode where it's mentioned. This is subtly lampshaded — Jet angrily asks Spike why he's running off to kill a man from his past. Spike pointedly (even cynically) asks him how he lost his arm, causing Jet to clam up. The circumstances behind Spike's pursuit of the man and Jet's lost arm are eventually revealed.
• Eureka Seven:
  • This anime features the characters spouting a lot of Gratuitous English phrases that won't mean anything until a good twenty episodes later. It gets pretty confusing when half of the spoken terms have no meaning to the viewer.
  • Its sequel, Eureka Seven AO is slightly better. There are a lot of references to events in the past, and several hints that there is something off about the Alternate Universe. They also managed to cut the introduction to meaning rate by about 50%, meaning that almost every truly cryptic and bizarre thing has been given some measure of explanation or meaning within 10 episodes, as opposed to the 20 mentioned above. Yes, if you just started watching, that means that the Alternate Universe thing will get explained very soon.
• This is a big part of what makes FLCL such a Mind Screw. Naota (and the viewer by extension) is essentially dropped into the middle of some huge, epic Space Opera story and almost never has any of the events or backstory references explained to him in a fully coherent way. In keeping with with the coming-of-age themes, the broad experience of the show is comparable to being a young kid growing up while some war is being fought in a foreign nation, with your only understanding of it coming from the adults in your life who barely know any more than you.
• My Hero Academia: Shoto Todoroki's backstory reveals he has three siblings. The second oldest, his sister Fuyumi is introduced after the Sports Festival and their middle sibling, Natsuo, is introduced when the manga is about 180 chapters in, but their oldest brother is not even mentioned. In chapter 192 when Natsuo refuses to hear to the apology of their Abusive Parent Endeavor, hints finally start being dropped, including that the older brother is named Toya and "something" that happened to him by which Endeavor is (rightfully or not) blamed for and that has fomented their mother's breakdown.
• The Hidden Cloud Village in Naruto was introduced long after the other four major ninja villages. The only proof of their existence was that a small number of Cloud ninja applied for the Chunin Exams early into the series, and after that, they were completely absent for several important arcs. The Hidden Cloud Village was even nonexistent among the Akatsuki, an alliance of villains from various ninja villages who have disowned their home villages in protest. This becomes a plot point later on after the Hidden Leaf Village is destroyed by Akatsuki leader Pain and the village leaders gather together to discuss how to stop them. As the Akatsuki has no Cloud ninja and they've never attacked the Hidden Cloud Village, the village leader makes it clear he has no reason to get involved.
• Negima! Magister Negi Magi:
  • A visual one: in the splash page from the first chapter of the manga, look closely at the center. Zazie Rainyday has claws.◊ 250+ chapters later, this is still unexplained, as is everything regarding Zazie. It finally appears in the story proper in chapter 298.
  • The Magic World is filled to the brim with this type of stuff, with people referring to all sorts of races, animals, places, and phenomena that don't happen here.
• The first thing everyone knows about Pokémon: The Series is that most Trainers dream of becoming a Pokémon Master, however over the entire course of the series it's never once discussed how one actually obtains this title until the very end with The Pokémon Company outright refusing to elaborate.
  • Due to comments made by Lance in Pokémon Red and Blue the initial assumption was that becoming the Champion of a region makes one a Master, however, Ash explicitly states later on that it's merely a prerequisite and considers himself to be a long way off even after becoming the Champion of Alola. Even Memetic Badass Red still has the Trainer Class "PKMN Trainer" in the games after everything he's been through.
  • In Pokémon Journeys: The Series Goh asks if being a Master means becoming the strongest Trainer with Mewtwo's comments in Pokémon: The First Movie seemingly supporting this theory, but Ash states not even that is enough. In fact, Champions Wallace & Cynthia are recognized as the strongest Trainers in the world and undefeated Champions (until the former lost to Steven and the latter Ash), but they're only "Champion Masters". However, once Ash himself earned the title of strongest Trainer he apparently became that much closer to his goal. In Pokémon: To Be a Pokémon Master he finally decides that being a Master means seeing the world and meeting all the Pokémon in it, with him deciding to continue Walking the Earth.
• Puella Magi Madoka Magica:
  • A very subtle one. When Mami explains why Witches are bad, she mentioned them luring people to suicide and causing fights to break out in certain places. The second type of bad influence is never seen in the anime.
  • It's also hinted that she knew Kyoko, and Kyoko's past — but this is actually confirmed in a Drama CD.
  • Several are found in in the manual(s). The official website describes three witches who never appeared in the anime, because only their familiars did. We don't even know what they look like. Then we have the revelation that Walpurgisnacht is only a nickname. It's real name is only listed as "?????".
    • Of course, Mami also mentions that Witches cause "natural disasters" in addition to the suicides. And Word of God about Walpurgis is that it's actually a Witch that grew stronger by combining with other witches.
• In Psycho-Pass, there are very occasional references to the fact that some great catastrophe has happened and Japan, with the aid of the Sybil system, is one of the few relatively normal nations left.
• Slayers has a hierarchy of gods and demons distributed over four universes. Only some of these deities are described, others are named or merely implied. Nothing is known about the demons Chaotic Blue and Death Fog, for instance, and less than that about their opponents. Fanfic authors have, naturally, expended much effort to fill the gaps.
• Sound of the Sky is rife with this trope. Most of the back story can be divided into two categories. There's the information that was lost forever during the Great Off Screen War, which isn't explained since none of the characters are aware of it. And then there are the things that all of them know about, which isn't explained since the characters have no reason to exposit out loud about it when speaking to each other.
• Yokohama Kaidashi Kikou is the Slice of Life story of a Ridiculously Human Robot named Alpha running a small cafe during the twilight of humanity. Numerous mysteries are touched upon but absolutely none are explained fully, either because they have nothing to do with the story as previously outlined, or the characters are just as much in the dark as the readers.