Norse myths (Kanade's relic, Gungnir), Japanese myths (Tsubasa's relic, Ama-no-Habakiri) Hebrew/Sumerian tales (Kadingir, the gateway of the gods, looks like the Tower of Babel, the healing artifact Nehushtan and the demon-binding Staff of Solomon), Roland's sword Durandal, all together.
All mythological creatures and monsters are thought to have existed too, though the majority are theorized to have been Noise.
All There in the Manual: Lots of information regarding Symphogears, relics, and other material can be found in the form of translated key words. They give insight to things that weren't or couldn't be explained by watching the anime alone.
And the Adventure Continues: At the end of the series there's still Noise in the world to be fought and heroines willing to do it. Indeed, the adventure continues in Symphogear G.
Kanade and the main heroine, Hibiki in the very first episode. That said, it turns out Hibiki wasn't actually dead.
Of diplomatic importance, Japanese Defense Minister Hiroki is assassinated in episode 5.
Badass Family: The Kazanaris. Tsubasa is a Symphogear trained since childhood to become a warrior (or a sword/sentinel according to herself), and her uncle, Genjuro, is a Badass Normal who punches boulders and gets all his training from watching action movies. By extension, the latter is also Chris' legal guardian, who reveals herself to be another powerful Symphogear user.
Bait-and-Switch Credits: Subverted. The last thing you will see in the OP is the holding hands of two girls and a starry sky. This is elaborated further in the finale, and it is also the last thing you will in that episode. After Hibiki's return to Earth, she and Miku get to see the meteor shower, holding hands.
BFS: Durandal. Hibiki activates it in episode 5, which she promptly uses to demolish an entire chemical plant in a single attack.
Just as Hibiki did in the first episode, in the last episode Miku rescues a girl under Noise attack, they run, she falls, a heartbeat is heard...
The whole graveyard scene serves as book ends.
The final episodes (of the first season) bring back the following songs: Synchrogazer (as an ending theme specifically) and Gyakkou no Flügel (the insert song from the first ep, now the series ending theme).
Done again in the final episode of the second season with: Vitalization (as an ending theme for 12) and Niji Iro no Flügel as the series' ending.
Body Horror: Noises' mere touch turns people into ashes quickly, but not quick enough for the victims not to feel it.
The first episode is very dark. The second episode is far brighter, focusing on Hibiki's induction as a Symphogear candidate; then episodes three and four go back to being serious... until the very last minutes of episode four suddenly turn into a goofy shonenTraining Montage. Overall the tone of the series gets Lighter and Softer as the series progresses (Episode 8 even relies on The Power of Love and The Power of Friendshipas a plot point) with the international conspiracy subplot and Chris' Dark and Troubled Past being the only "edgy" elements left by the finale.
The 2nd season, on the other hand, goes back to the dark tone of the first 4 episodes, and even more.
Chekhov's Gunman: The little girl Hibiki saved during episode 1 plays a role in the finale.
Cliffhanger Copout: Tsubasa and Hibiki's fight never happens: old man Genjuro comes out of nowhere and stops Tsubasa with his BARE FIST.
Colony Drop: This was Finé last ditch effort as she grabbed a piece of the moon and pulled it towards the Earth. The second season reavealed that the moon itself is heading towards the Earth.
There is at least one Dead Star Walking character, who dies in episode 1 of both seasons.
At the end of the respective first episode, a new Gungnir user appears, followed with Genjuro's reaction "Gungnir datto?!"
In season one, Hibiki breaks off the heels of her Symphogear outfit because they're in the way. Season two has Tsubasa accidentally break a heel of her idol outfit when fighting Maria.
When Hibiki tries to prevent Tsubasa and Chris from fighting in episode 4, they say "Shut Up! This is a battlefield!". This happens again in G, this time it's Shirabe and Kirika.
Episode 12 from both seasons start with the ending theme and end with the opening theme. At the end of the episode, Hibiki transforms and she yells "SYMPHOGEAR!" and "GEKISŌ ・ GUNGNIR DA!" in response to Finé and Maria, respectively.
The first season ends with the song Gyakkou no Flügel. G ends with Niji Iro no Flügel, a remix of the former.
Creature Hunter Organization: The Mobile Disaster Response Corps, being the ones with Symphogear users who are the only ones with a fighting chance against the Noise.
Eagle Land: Extremely obvious by the phone call and the assassination of Hiroki by anAhnuldlook-alike. — In-universe, Japan and America relations are tense due to sheer competition and its authority present around the world. At least until it is revealed that America and Japan were working together to get information about Ryoko.
Chris is added to the final group shot in the OP in episode 11.
In Symphogear G, Episode 5 adds portraits of the legends the gears are based on and episode 10 adds Miku with her Symphogear.
Expy: The Noise; they're the Gnosis in all but name. Namely, they resemble featureless humanoid or animal-like abominations, shapeshift, can go right through walls and conventional projectiles, turn humans into swiftly crumbling statues on touch, and may only be harmed in the split second while they attack - unless specialized weaponry based on ancient artifacts is used.
Faux Fluency: The beginning of episode 5 has a conversation over the phone done in full English. And it's very obvious the voice actors aren't very fluent in the language. Watch it here. Invoked on the Japanese side of the conversation: she was performing that gratuitousness as an insult to her American interlocutors.
Miku's Symphogear Shenshou Jing possess similar color and ability to Kamen Rider OOO's Putotyra Combo.
Many of Tsubasa attack is similar to Kamen Rider attack such as her Heaven’s Wrath attack that somewhat resemble variation of Kamen Rider Gattack's Rider Kick and her Flash of the Rider's Blade which similar to Rider Break attack
Image Song: Not only the Symphogear users has some, even minor characters gets image songs in G.
Innocent Fanservice Girl: In G episode 12, no less than three characters suddenly find themselves naked due to their circumstance. Two of them are even displayed in their glorious nudity to the whole world!
Noise are nigh-unbeatable for anyone who doesn't have a Symphogear. They can kill in a single touch, and are only vulnerable to conventional weaponry within the split second in which they need to physically interact with their target.
MacGuffin Delivery Service: In G, Hibiki and Chris' battle to secure the by-train delivery service of a relic is rendered moot when the Noise attack the party who receives it just as those two leave. Both the relic and the scientist who handles it (Dr. Ver) are missing. Episode 3 says that this was intentional, and that Dr. Ver is actually in league with the Big Bad. No, he is the Big Bad.
Magic from Technology: The relics are explained as ancient supertechnology by Ryoko. Then again, she's a reincarnated Sumerian priestess who wants to break the Curse of Babel.
The Men in Black: The government agency handling the Symphogears actively keep their existance from the public eye, as they are considered a strategic resource. But their tactics are pretty nice and polite, like making witnesses sign Nondisclosure agreements.
No Sense Of Energy: Dr. Ver exclaims that the energy released by Nephilim's heart that will vaporize the earth exceeds 1 trillion joules. This is roughly equivalent of 1 kiloton of TNT, or a third of the energy released in the Halifax Explosion of 1917. Of course, he does have a few screws loose so his thinking could be off...
Off Model: Episode 3 has a walk scene that looks animated in Adobe Flash. The animation studio working on Bodacious Space Pirates in the same season (especially when Mouretsu Pirates has so much CG scenes in them), plus having the OP single delivered post-haste and a budget slash might explain these animation issues.
Phenotype Stereotype: Notably, given how notorious anime is for this trope, it's averted for the most part. Maria and Serena do have bright blue eyes, but lack the blonde hair that's also typically associated with Americans and other Anglophone countries. Nastassja, Dr. Ver, and Chris all lack both the stereotypical hair and eye color. Background characters who are said to be American aren't overwhelmingly blonde and blue eyed either. However, it's played straight in regards to Finé once you realize that she was apparently blonde and fair skinned even though she lived in Ancient Mesopotamia - located where Iraq stands today. It makes more sense while she's using Ryoko's body if you take Power Dyes Your Hair into account, but she has the same hair and skin even when you see the real Finé during flashbacks and when she speaks to Shirabe from within her mind.
This was actually played with a few times. They used it to announce a special event after the credits of the final episode of season 1, and Genjuro's reaction changes from a yell of surprise to quietly repeating the name of the Relic with a worried look at one point in season 2, when Hibiki's uses her Gungnir when it could kill her.
Scenery Porn and Scenery Gorn: On both sides of the spectrum, and can change at any moment. Transitioning from a vibrant laser-show concert that ended with a sunset to a battle-stricken concert under that same sun is animated very beautifully.
Second season adds up 'Maria' and 'Shirabe' in the shout-out to said familiar series.
When Tsubasa bleeds from eyes and mouth when she executes her Ultimate Song against Chris, she looks almost like Miki Sayaka during her "I'm such a fool" moment. Jarring, because Tsubasa normally doesn't make that kind of face, her emotional spectrum considered.
At one point during the episode 4 Training Montage, Genjuro is dressed exactly like Akuma/Gouki. Considering his Badassery, it's not exactly inappropriate. Hibiki is also wearing Makoto's clothes.
The Training Montage of the second season, on the other hand, is a full-blown Shout-Out to Rocky, complete with punching frozen carcasses and the library staircase.
Chris's armor the Ichaival is a nice one to Wild ARMs.
Let's not forget "pagan technology", the "Ruins of Memory" and Kadingir, a tower to reach the heavens.
Miku's Sympohogear form is a pretty much a Murokumo unit, mixing elemnts of Nu-13 and Lambda 11 (the Anubis-like head gear and visor) with elements of Mu-12 (having special devices that allow beam spam).
The final episode of G. Vitalization? They might as well have called it Hell and Heaven!
Starts with Their Funeral: The first few minutes of the first episode reveals under Grave Clouds that Hibiki is already dead and buried. The series then flashbacks to two years ago and then forward two years again (though some time before the initial scene, since Hibiki's still alive) to show it got to that point. Also doubles as a Foregone Conclusion.
In season 1, Genjuro states that Japan has the upper hand over the crisis-ridden Europe (i.e. the 2008 financial crisis), and thus the Durandal will be kept by the Japanese.
In season 2, Genjiro states that the USA can't be trusted. One wonders whether it's because the mess was kickstarted by the American relic lab, or due to the sheer extent of the US' surveillance state in Real Life.
Tempting Fate: Pretty much all of the first half of episode 10. "Boy do I like my school! I sure hope nothing happens to it!" Well guess what?
Those Three Girls: Aside from Yumi, Shiori and Kuriyo, there are also three girls in Chris' class that want to be her friends and help her break out of her shell.
Title Drop: The collective name of the anti-Noise armor is the name of the show. And the Ultimate Songs are translated from the the Japanese word "Zesshou". Also, each season title-drops its opening theme as the final, ultimate attack for that season.
Tokyo Is the Center of the Universe: Japan as a whole consists of the Research Facility underneath the school, at least three Symphogear users in two locations, and (potentially) two weapons, one of them being BFS Durandal. Doesn't look like Japan will hand over Durandal to the EU, what with Episode 5's revelation that Hibiki can use it as part of her song.
Tower of Babel: The tower Fine built to reach God is obviously supposed to be it, despite being unnamed within the show. But since she mentions the Curse of Babel too, it's obvious. Finé even transforms into the semblance of the Whore of Babylon when she goes One-Winged Angel, with apocalypse dragon included.
Wave Motion Gun: Kadingir is not a tower - Finé even references the biblical Shinar - even though it is referenced as such, but an humongous energy cannon with the intention of shooting the moon. It works, but not as expected.
Weird Moon: It... has a massive dent and a ring surrounding it as shown early on in the second season.
Episode 11; the Big Bad and her plan is revealed, bad guys change sides or turn to have been The Mole for the good guys all along.
Symphogear G, episode 5: The moon is on a collision course with earth, and Hibiki loses an arm to the Nephilim.
Symphogear G, episode 7: Maria didn't inherit Fine...but Kirika does.
Symphogear G, episode 9: Miku was brainwashed by Doctor Ver and armed with her own Symphogear.
Symphogear G, episode 10: Hibiki and Miku are apparently killed, The Frontier is risen by their fight, and as a last shot Chris shoots Tsubasa in the back while saying "Goodbye"
Whole Costume Reference: During Hibiki's aforementioned training montage with Genjuro, there's a brief still where Hibiki dressed like Makoto (the red cloth strip is on her neck and her gi isn't sleeveless) and Genjuro dressed exactly like Akuma, both characters of Street Fighter fame.