Attack on Titan first began way back in 2009 as a manga, chronicling the life of a young boy called Eren Jaeger. He lives in a unique post-apocalyptic society, a city surrounded by giant, mysterious walls to keep out a horde of even more mysterious humanoid monsters called Titans. As the series progresses, we learn more and more about this quirky premise, eventually gaining insights into all archetypes of characters that populate the world. The big secret, of course, is where the wall, the Titans, and the characters' transformation powers came from.

The show itself can be considered dark fantasy, and the secrets it holds are no exception to this theme. From interviews with the creator to subtle hints in the manga/anime itself, there's tons of info beneath the surface of this incredibly popular franchise. All it takes is a bit of digging. As of now, two seasons of the anime have been released, though the manga goes a little further. A fair number of big mysteries have been revealed, though plenty of plot secrets remain hidden, the subject of nothing more than fan theories.

It goes without saying that there may be spoilers, so if you haven't seen the latest season, bookmark this one for later!

20 Too Soon?

via: FUNimation

In a guidebook released for Attack on Titan, all the main characters' birthdays were revealed (dates, not years). Additionally, each date holds some level of significance culturally, numerically, or in the case of Marco Bott, referentially. His birthday is June 16th, which just so happens to be exactly in the middle of the year. This is both funny and dark, given the way Marco does. He is found dead with only half his body (the left half) remaining. The rest is assumed to be either eaten by a Titan or scattered somewhere else in the city.

On the subject of birthdays, Armin was born on November 3rd, which is known as Culture Day in Japan, somewhat appropriate given Armin's deep love of learning and interest of life beyond the wall.

19 The Dead Mom Hairstyle

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If you're a seasoned anime fan, you're probably familiar with the iconic mom hairstyle worn by characters such as Trisha Elric from Fullmetal Alchemist, Ikumi from Bleach, and even the mom from My Neighbor Totoro. Each of them have a low maintenance look with a small braid hanging over their shoulder. It's a classic anime "caring and gentle "mom look, depicting how they're too busy being mothers to worry about appearance.

However, fans have noticed an even darker theme surrounding this hairstyle: every mom that has it is either dead or about to die when the series begins, and Attack on Titan is no exception. In fact, she and Trisha Elric are voiced by the same person! Why do the moms of main characters die in almost every anime? No one knows, but tragedy usually acts as a catalyst for character development.

18 A Pretty Dark Theme Park

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With a story about flesh-eating giants roaming the Earth, subjecting victims to what is possibly one of the most horrific deaths imaginable, the logical next step is to build a theme park around it. In Universal Studios Japan, you'll find an experience dedicated to the massively popular anime. The level of detail that went into designing the massive Titan sculptures is terrifyingly good, with the main attraction being actual-sized statues of Eren's Titan and the Female Titan locked in combat.

Visitors can even experience the traditional Survey Corps meal, which includes soup, bread, bacon, and a potato: the heartiest meal of the post-apocalypse. Perhaps the most uneasy thing is an exhibit designed to allow guests to stand in the hand of a titan, with a massive head right besides them, ready to chomp down. So it's a horrifying death in the show, tourist attraction in real life.

17 It's All Japanese Propaganda

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Around the time the manga was first released, Isayama confirmed that Dot Pixis, one of the military leaders, was based on a real-life Japanese general named Akiyama Yoshifuru. During Japan's imperialistic years, he was the commander of an occupying force in Korea. There, he established a strict regime and committed a fair number of war crimes including torture and slavery. Therefore, Koreans view Yoshifuru as a war criminal, and the Korean fandom of the show was quite unhappy with Isayama's reference. In fact, he received a few death threats.

It's somewhat ironic that one of the good guys in the show is based on a rather disliked historical figure. Even Erwin, another protagonist, is based on a Nazi military figure, as we'll see later.

16 The Female Titan Doesn't Make Biological Sense

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You might have to think back to high school biology for this one, as far back as that might be. As we know the normal Titans are humanoid but none of them have a gender, or even reproductive organs. However, they all look masculine; broad shoulders, square jaws, and other features that are typical of an XY chromosome (XY is male, XX is female). However, in humans, upon which Titans are based, this makes no sense. In the womb, we all develop as girls until some point when, if we have the male chromosome, our body produces testosterone and turns some of us into guys.

So it begs the question: why are Titans depicted as males? And the natural follow-up: Why is being a female Titan the special case? Shouldn't it be the other way around? Most can probably chalk it up to artistic liberty, but others might consider it straight-up sexist (though, against which gender is unclear).

15 A Tragic End To A Tragic Musical

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One might say it's more of a Bollywood thing, but musical theatre is very popular in Japan. From modern musicals to anime-based works like Death Note: The Musical, the culture surroudning it is vast as it is spectacular. So it's no surprise that the wildly popular Attack on Titan was also set to have its own spin-off musical, scheduled to run for a couple months this past summer. However, the show was over before it even began, due to a fatal accident on set.

Kazutaka Yoshino, one of the acrobatics, was testing the stage wires that would be used for the action sequences of the show. However, it snapped mid-air, causing him to fall about thirty feet. He was rushed to the hospital, but unfortunately pronounced dead soon after arrival. The project was then cancelled.

14 Tears For Sasha

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Another protagonist, Sasha Blouse, was supposed to be killed off in the manga in Volume 9. An entire chapter was meant to be dedicated to her, ending with her death, a fitting send-off to be sure. But Isayama was apprehensive about going through with it. In fact, one of the editors apparently cried after reading the original draft, convincing the creator to go with a different route.

The editor later said that Volume 9 wasn't the right time for Sasha to die, that it was too early. This suggests that Sasha was saved this time, but her death is all but inevitable. Then again, so is that of any character in this unpredictably dark series.

13 Eren Jaeger, I'm Here To Talk To You About The Avengers Initiative

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Crossovers are common and often celebrated in American culture. Whether it be films, television, books, or comics, we always love to see our favorite characters interact in a shared universe. This is much more rare, however, with Japanese manga. Yet, for Attack on Titan, the publishers made a rare exception.

As we all know, the Marvel Cinematic Universe is based on the veritable library of comic lore. Similarly, Attack on Titan is based on its respective manga. In 2014, when the latter had become fairly popular, Marvel made a deal with Kodansha (publisher of AoT) to create a crossover comic called Attack on Avengers, which showed the Titans attacking the city of Manhattan. Much like in The Avengers, the main squad gathers to defend the city against the onslaught. Near the end, the notorious Colossal Titan arrives, threatening to destroy the city with one fell step. At this point, who else but the Guardians of the Galaxy heroically arrive to battle it.

12 Popularity Contest

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The main protagonist of the series is initially Eren Jaeger, with the entire cast gaining more screen time as the show goes on. It's a true testament to the quality of the writing that so many characters can each act a part of their own plot, rather than simply being side characters in a singular main character's story.

That being said, the popular characters of the show may surprise you. Based on popularity polls, the most popular character is actually Levi, thanks to his stoic demeanor and chill attitude towards literally everything. Eren comes in second place, given his "generic anime hero" status, and Mikasa is third, despite the fact that she's arguably an overall cooler character than Eren.

11 Mikasa's Name: A Respectable Joke

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The creator believed that naming female characters after Japanese battleships was good luck, based on certain previously successful mangas. Therefore, he named Mikasa after a battleship built in 1902, the Mount Mikasa. The nomenclature makes sense, given that she earned the #1 rank in her class and was once said to be "worth a thousand soldiers." She's also a genius and really good at singing.

Her status as probably the most high-functioning human being in the show and possibly real life makes the literal translation of her name somewhat ironic. "Mikasa" actually means "three bamboo hats."

10 The Titans' Real-Life Counterparts

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Remember those spoilers we were talking about? Here's a few of them. As we've learned in the earlier seasons, each of the "special" Titans is actually an alter ego of one of the main characters. There are nine such titans in all, and they possess appearances and abilities that differentiate them from your average Titan.

Each of these unique mannerisms are actually based on people in real life. Eren's Titan was inspired by mixed martial artist Yushin Okami, partly in appearance and mostly in fighting style. The Armored Titan, controlled by Reiner Braun, is based on Brock Lesnar, a professional WWE wrestler (and also a mixed martial artist).

9 Allusions To Watchmen

via: Warner Bros.; FUNimation

While we're on the subject of character inspirations, there are two characters in Attack on Titan based off the Watchmen series from DC Comics. Levi's character was actually a confusing combination of multiple other characters, but his personality was based on Rorschach from Watchmen; both have a cynical and often emotionless disposition. However, his short height is based on Astroboy and Kyuzo (from the film Seven Samurai) and his name comes from a character featured in the American documentary Jesus Camp.

Erwin, the Commander of the Survey Corps, was based on Ozymandias, also from Watchmen. Both are natural-born leaders with powerful stature and mature tones about them. However, his name (and part of his personality) comes from Erwin Rommel, a Nazi general from WWII. Erwin's birthday is October 14th, which is also the date Rommel died.

8 Smell Like A Titan-Slayer

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Besides a questionably designed theme park, every great franchise has its own merch. Attack on Titan is no exception; in fact, the most infamous example might be a figurine of Levi that sold for over $7,000. Multiple other action figures from the series are also available as collectibles.

But a stranger line of products has to be their signature perfumes. Each character has their own unique scene: Levi the clean-freak has a fresh soapy aroma, the innocent Armin Arlert has a pure vanilla scent, and the quirky Zoe Hange apparently smells like a mysterious, bitter herb.

7 Parallels To Norse Mythology

via: norsemyth.org

The creator is Japanese, and most characters are German, but the story itself has roots in Norse mythology. Quite early on, Armin talks about what he thinks is beyond the wall, which include a sea of flames and a field of ice. In Viking lore, the realm of Muspelheim is the former, and Nilfheim is the latter. There is also Jotunheim, which is the home of giants, and finally Midgard, or as we call it, Earth.

As the stories go, the gods built a wall against the giants from the eyelash of Ymir, which is also the name of a character in the show. When Ragnarok happens, or the apocalypse from more contemporary religions, the giants break down the wall and kill the gods (essentially the plot of AoT). This ties in nicely to the background of Eren's father, the Nine Titans, and much more. You can read all the details on this Reddit post.

6 Attack On Subaru

via: Subaru

Let's just say advertising culture is much more different in Japan than it is here. With the growing popularity of the anime and manga, the logical next step seemed to be depicting the horrifying Titans in poor CGI and putting them in a commercial for the Subaru Forester.

This crazy advert shows a driver escaping a group of Titans in the aforementioned car, driving down a windy hill pursued by rock crushing monsters. The Colossal Titan even makes a last-minute, albeit anti-climactic, appearance. If you're so inclined, you can watch the 30-second ad on YouTube.

5 Levi's Real Rank

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The soldiers call him Heicho, short for Heishicho, which means "leader of soldiers." This is somewhat odd, since in Japanese military this is the rank of Lance Corporal, which is relatively low on the chain of command. Still, this may go along with the fact that he isn't an official member of the military, but a special operative that sort of does his own thing. Similarly, Erwin is often called "dancho" which translates to Commander, though this fits his status as the actual leader of the Survey Corps.

To add to the confusion, Levi's real age is never revealed. He may seem like someone in his mid-20s (despite being only 5'3") but according to Isayama he is deceptively older. His birthday is December 25th and he's "at least 30"; those are the only clues we have.

4 Jean Is A Represenation Of Humanity

via: FUNimation

In the opening sequence of the anime, you'll see a soldier in 3D-maneuver gear performing a sick flip. Most might've assumed this was Jean, but the creators originally meant him to just be a generic soldier that was an "anonymous representation of humanity." However, so many people considered it to be Jean that the creators acknowledged it. They even included a scene where he performs that exact move on the Female Titan.

Interestingly enough, Jean Kirstein is also Isayama's favorite character from the franchise. He appreciates how the character always speaks his mind, with little regard to the consequences. I supposed honesty and bluntness is important in a post-apocalyptic society.

3 It Might End With Everyone Dying

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The success of Attack on Titan is almost unprecedented. For a single-season anime to gain that much popularity, and even its own theme park attraction, is insanely impressive. Even the creators themselves were surprised, which is why there's such a long gap between season 1 and 2; they didn't plan on the level of success.

With great power comes great responsibility, at least for the creator. There are still numerous questions the show has yet to answer, and the horde of fans are getting impatient. Despite this, Isayama has openly admitted that he wants to end the series with the main cast dying and the plot left unresolved. The show is dark enough as is, and such an ending wouldn't be totally out of the question. Still, he says he's not likely to do this given the possible negativity that would plague him with such a bold move. Had the series been significantly less successful than it was, then he might've actually gone through with that original plan.

2 Or It Could End With Just Armin

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You may have noticed that Armin Arlert and the narrator of the anime are voiced by the same actors (Marina Inoue in the original, Josh Grelle in the dub). While it's possible those voices just happened to be the best for narration, it seems somewhat implausible given that the voices are quite different (the Japanese voice for Armin is that of a woman).

This, coupled with the fact that Isayama has openly admitted to considering killing off the main characters, suggests a darker ending in store for us. It follows that Armin is the only surviving member of the original cast, which is why he's doing the narration several years in the future (from a book or possibly just as a story) rather than someone like Eren or Mikasa.

1 Hajime Isayama Is Way Petty

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Hajime Isayama is the creator of Attack on Titan. However, he didn't write the manga alone. Generally, while creators write the story and work on the bulk of the drawings, they have a team of artists that finish each page, adding details and color. These assistant positions are still quite prestigious; they are seen as an important stepping stone into the world of manga, and many famous manga creators started out that way before making it big.

Interestingly enough, one of the assistants on the Attack on Titan project left the team when they got their own manga published. For old times' sake, he asked Isayama to draw a cover for the romance-themed story. His old boss instead drew the hilarious depiction you see above, a female Titan eating what is assumed to be the male love interest alive.