The way the Emblems are introduced throughout the plot harkens toward certain elements of their respective home games:
Marth, being the first Lord in the franchise, is the first one players interact and familiarize themselves with, and his first bearer is naturally the main character of this game, Alear.
Sigurd is introduced by Lumera, who is also a parental figure to one of their games' main characters (Seliph and Alear). In a bit of a dark note, much like how Sigurd infamously dies by the end of his game's first half, Lumera is the game's first named casualty, setting up the player's journey to collect the rings.
Celica is first introduced when the player is being introduced to the Kingdom of Firene, a region which advocates for peace and helps others in need. Like the kingdom, she is known for her pacifistic behavior and her eagerness to help others, traits that do drive a wedge between her and Alm regarding how to resolve the conflict in Valentia.
Micaiah is introduced after the player retrieves her ring with the help of a thief named Yunaka. Prior to the mission, Yunaka mentions how Micaiah spoke through her ring towards her, much like how Yune spoke through Micaiah in Radiant Dawn's final arc. Not to mention the first three letters of Yunaka's name (a nod to Yune) and her class as a thief (a nod to her Love Interest Sothe)
Roy is first introduced during the backdrop of the Brodia/Elusia conflict, not too dissimilar to the invasion set out by Zephiel which kickstarts The Binding Blade's events. In addition, Roy's first bearer is Diamant, who is also a sword-wielding, redheaded Lord.
Leif is introduced in the same chapter as Roy's, befitting that they're both from the second generation of their respective sagas.
Lucina and Lyn:
Both are introduced in the middle of the game's Darkest Hour, after the player had lost all their rings only for Princess Ivy offer the group some hope in the form of the Time Crystal and two Emblem Rings. This was Princess Lucina's mission in her home game: to give hope to the Bad Future she came from.
It also ties in with when Lucina is first introduced as a Dark Emblem, as the events at that time are similar to one of Awakening's key events: a good kingdom (Ylisse/Firene) asking help from an aggressive nation (Ferox/Brodia) against the antagonistic faction (Plegia/Elusia). There is also a mistake at the border where Ferox/Brodia mistake your party for bandits (Although Engage doesn't have you fight Brodia).
Lyn (at least in a non-Dark Emblem state) is also introduced by Princess Ivy in the same chapter. The chapter of The Blazing Blade that reintroduces Lyn into Eliwood's and Hector's stories starts off with Florina, a Pegasus Knight, who is looking for Eliwood and Hector to inform them that Lyn and her army wish to join up with theirs. While not a Pegasus Knight, Ivy is still a flying unit who joins her forces with Alear's. Ivy from that point onward also has the goal of taking back her home territory, like Lyn before her, and her antagonistic father even bears a striking resemblance to Lyn's antagonistic granduncle. Both of these antagonist male relatives were even willing to spill the blood of their own kin in one way or another. note Lundgren would have gladly killed his own grandniece and brother if it meant he could have complete control of Caelin, while Hyacinth sent Ivy out to battle against Alear and company without an Emblem Ring after she failed to capture Brodia Castle with a ring.
Both are also from games that opened the series to new audiences: The Blazing Blade was the first game to receive an English localization, and Awakening caused a Newbie Boom that saved the franchise from being shelved altogether. Of course these would be the Emblems Alear receives to replace the ones Sombron stole!
Ike is introduced in the middle of a bandit attack where they destroy a house. Ike's first real battle in Path of Radiance also involved that.
Byleth is given to you with Hortensia who decides to defect from Elusia to fight alongside your party. During the first part of the Black Eagles route in Three Houses, you are given a decision to fight with the Church of Seiros leading to Silver Snow, or ally yourself with the empire segueing to Crimson Flower. In both cases you break off from one faction to join the other with your remaining students supporting your cause.
Corrin is introduced aiding the game's Dancer unit, Seadall. Fates' deuteragonist, Azura, is essentially a Dancer in functionality, and she and Seadall share similar hairstyles. Additionally, Seadall, whose name sounds a lot like "see it all," is a fortune teller, so it can be said he's able to see another's fate.
Eirika is introduced in the desert lands of Solm with Rosado and Goldmary, the final retainers you recruit in the game, who reunite with their liege Hortensia. In Sacred Stones, Eirika and Ephraim also reunite in a desert map. In said map, the twin whose route you did not choose will join you with two characters exclusive to his/her route, and the two bosses on the map are a Hero and Wyvern Knight, just like Goldmary and Rosado.
The obvious pun is obvious; a person wears a ring on their ring finger to show that they're engaged.
It is only after players played the game once that they see the full context, but there is a scene early on where Alear's past as Fell Dragon heritage is subtly revealed. In Chapter 2, Lumera explains to Alear the story of the 12 Emblem Rings and how they, as the Divine Dragon, can summon heroes from those Emblem Rings. Alear assumes that it is the invocation that allows them to summon Emblems, but when Lumera hears this, she thinks for a moment before asking about Alear's intention when they summoned Marth - they reply how they wanted to protect others because they didn't want to lose them. Lumera then replies that they must not forget that intention when they summon Emblems, so that they remember that they're borrowing the heroes' power to protect others rather than to keep the power for themselves. Players might initially think Lumera's advice as nothing out of the ordinary, but considering the reveal later, she must have suspected that Alear might not have been entirely cleansed of the Fell Dragon's power (despite her efforts to the contrary). This is because Griss, one of the Four Hounds, figured out that Alear is the child of the Fell Dragon from how they summon Emblems: although both Divine and Fell Dragons can summon Emblems, Divine Dragons pray while Fell Dragons invoke (which is actually foreshadowed when Lumera doesn't use an invocation in her mock battle, but Sombron does when he steals the party's first six rings). Lumera must have realized this way back when, but she chooses not to say anything because she didn't want to burden her adopted child Alear with the truth about their horrible past/heritage. She then must have considered their amnesia as a hidden blessing, because this allowed them to believe that they were the only child of the Divine Dragon, instead of a child of the Fell Dragon.
A brilliant bit of Foreshadowing occurs at the beginning of the game when Alear is disturbed by the Fabrication warriors Lumera animated for them to practice against. It only makes sense that, as a half-Divine and half-Fell Dragon, they’re unsettled by the Fabrications of Lumera as they are the Corrupted of Sombron.
At the end of Chapter 18, Emblems that have gathered so far (Sigurd, Lucina, Eirika, Ike, Lyn, Leif, Corrin, and Byleth) have a discussion among themselves about whether to use a far greater power called the miracle that is not the usual power granting once every one thousand years. Some Emblems like Eirika suggest using it on Lumera, who has already died early in the story. Savvy players might have guessed that the effect of the miracle is some sort of resurrection by this point, but there is a moment where this was foreshadowed early in Chapter 3 where Lumera died. This is because when Emblem Marth laments about how if only they could grant their power now to save her, Emblem Sigurd tells him how they can't without other Emblems present. So with hindsight, this reveals early on how the miracle is some sort of resurrection power that can only be used when all Emblems are present. The full disclosure of the miracle's power is revealed in Chapter 22 when Alear is revived by becoming an Emblem as while the miracle can be used anytime, all Emblems have to agree on usage. Two demerits, however, are how not only this miracle could only be performed once and never again in the future, but also how it took all future power so there will be no more power gifting after this battle. All Emblems, however, all agreed to use the miracle because they all wished to fight alongside Alear.
A running theme of Fire Emblem characters is characters who look like young girls but are Really 700 Years Old dragons, like Tiki, Fae, Nowi, and Flayn. This time, the ancient dragon that looks like a teenager is you.
When Alear finally becomes the Fire Emblem at the end of the game, embracing their Divine Dragon nature, their hair and eyes fully turn blue, putting them in line with their fellow protagonists like Marth, Sigurd and Ike.
When normal, the Emblems use their default colors, have blueish eyes, and glow blue. But, when corrupted, they have a red, gold, and black color scheme, have red eyes, and glow red. It makes a lot more sense when you find out that blue represents the ally and red represents the enemy, which had been a franchise tradition since the first game.
Perhaps a subtle bit of Foreshadowing, three of the four heirs of their respective kingdoms are associated with the Emblems their families guarded. Diamant with Roy, Ivy with Lyn, and Timerra with Ike, they can even have a conversation with them during their respective trials, but Alfred is the odd one out. Instead, it's Céline who's associated with Celica's ring. Unless Alfred is paired with Alear it's implied he dies of illness shortly after the events of the game, which would likely make Céline Firene's future queen by default. In other words, all four of the kingdom's heirs do have an Emblem ring in their possession.
Adding onto this, the game almost encourages you to stick Sigurd's ring onto Alfred the first chance you get. Sigurd being a mounted unit just seems to go hand in hand with other mounted units and has some of the best extra abilities outside of dragon units. In addition, your only other mounted unit is Vander, who is your Jeigan unit so he doesn't really need the extra buffs right now. Adding on that Alfred is the prince of Firene and first time players will almost want to put it on him. Considering Sigurd's ultimate fate, this could also hint towards Alfred's ultimate fate in the future.
It's a rather ingenious bit of Gameplay and Story Integration that Firene is the first of the kingdoms traveled to, and thus the one with its recruited characters at the lowest levels. Firene, Brodia, and Solm are in an alliance to prevent war from breaking out between the three, and the ring-shaped continent means that Firene's position between Brodia and Solm and opposite of Elusia means that it's rarely, if ever, invaded by Elusian soldiers, and thus the people there see less warfare. In fact, it's so rare to see fighting break out there that when the Corrupted start popping up everywhere and bandits start taking advantage of the chaos, its rulers need to ask Queen Lumera for her assistance in quelling the threat. By contrast, each of the other three nations is adjacent to an enemy kingdom. In particular, Elusia and Solm have the strongest recruitable characters, with all of their bodyguard characters being in Advanced Classes rather than Beginner Classes like Firene or Brodia.
Brodia's unusual weakness relative to Elusia and Solm seems incongruent with its role as the Kingdom of Might, but it's repeatedly noted to be a mountainous kingdom, and thus would have a lot of natural defenses, making it difficult for Elusia to invade it. In addition, the Princes of Brodia, Diamant and Alcryst, are shown to dislike their father's militaristic policies, and thus they and their bodyguards would see active combat much less often. The two Brodian recruits unrelated to the royal family, Yunaka and Saphir, would both have seen a lot more active combat as an assassin and the Captain of the Royal Guard, and thus both start off in Advanced Classes.
The Emblems all seem to be oddly "okay" with their state of being spirits in rings. They seemingly speak of their homes and friends from other worlds and yet do not despair of being separated from them for all time, instead being happy with helping Elyos. It's eventually revealed this is all by design, the Emblems were not truly heroes summoned from other worlds, rather they were formed based on heroes from other worlds. They often act as if they are the same person, but every Emblem knows this is not the case, and that they came into existence to serve the function of an Emblem to protect and guide a particular world. It is their very nature, and what they are happiest doing.
Why does Byleth's Divine Pulse skill turn a missed attack into a hit, even though it doesn't work that way in Three Houses, where retrying a battle after rewinding causes the same result? It's probably because here the effect is on a much smaller scale, and your unit can adjust the trajectory of their attack to accommodate for which way their opponent moves. As for why it won't work that way in Three Houses, not only is it because you're commanding other units, but for Byleth specifically maybe the Divine Pulse would rewind time too far back and changes too many factors compared to a more split-second reaction from someone synced with his Emblem.
In Byleth's Paralogue, he recounts the legend of Saint Seiros and, instead of a bonding experience, frames their battle as a test to prove Alear can use their power wisely. Given that Rhea was the closest being to a Divine Dragon Byleth knew in Three Houses, it's possible he's treating the battle as a Secret Test of Character to make sure Alear won't end up like her.
Given Sombron has been alive for thousands of years, it may seem odd that Emblem Marth would state he has a chance of finding the original hero the Zero Emblem was based on, but not the Zero Emblem itself. Sure, Marth is certain the Emblem died, but wouldn't this also apply to the original hero? But then consider that time is not synced in all the different Fire Emblem universes (it flowing differently being the method by which the child characters in the Outrealms in Fates grow up in time to participate in the war), and that settings like Heroes involve pulling the actual characters into their world (as opposed to the separate beings Emblems are) even if they died thousands of years apart from other characters they summon, and it does indeed seem possible that the original hero (or at least one universe's version of them) could be somewhere out there still alive.
Zephia probably made the Draconic Time Crystal. Considering upon defeat, she awards the party with a crystal that sends them back into the past, it is not too far of a stretch that she is the originator of the player’s rewind mechanic.
Solm is a DESERT queendom whose people are named after DESSERTS.
Why is Loptous the Dark Emblem representing Genealogy of the Holy War despite never being directly fought and the final boss of said game being Julius? Well, the person you fight at the end of that game is certainly more Loptous than Julius at that point.
Additionally, if one takes Sigurd to attack this particular Dark Emblem, Sigurd is the only emblem who doesn't immediately notice them - he is confused, before immediately figuring out that because Tyrfing has awoken, this must be the "Dark God" he heard about. Why wouldn't he? Because he didn't fight Loptous - Seliph and Julia did! Who's to say that if his ring was either of them, they wouldn't instantly recognise Loptous?
Lucina's incantation being "Reignite us" fits not just for her story (given that she traveled to the past to save the world from calamity), but on a meta level as well, because it was her game that reignited interest in the series. Appropriately, she also joins the team during the game's Darkest Hour to instill hope back into the group, much like how her game was released at a time of uncertainty for the series, only for Awakening to be a smash success that brought the series into the mainstream.
Most Emblems are named after the title of their respective games, but Byleth, the Emblem of the Academy, is one of the exceptions. Not only would Emblem of the Three Houses suit the Edelgard, Dimitri, and Claude Bracelet more (while they are known as the Emblem of Rivals, they are contained within the Bracelet of the Three Houses), but Byleth doesn't even hail from any of the titular three houses anyway, nor can he actually teach all three at once— his title reflecting his time as a teacher overall is more fitting instead.
Including the DLC, there are three Emblems that houses multiple characters. How they handle these characters show how their games utilize them.
The Emblem of the Azure Twins holds Eirika and Ephraim, however Eirika is emphasized over Ephraim, who doesn't interact with the party outside of combat. In Sacred Stones, the second arc of the game splits Eirika and Ephraim who do not reunite until the end of the second arc. You follow one of the two and the remainder of the game is told in their perspective. While you can switch between the two, Eirika is still the character used for the Emblem.
The Emblem of Rivals has Edelgard, Dimitri, and Claude, the three house leaders and future rulers of their respective nations. While you choose which house you follow, the other two houses still have relevance outside of their own route. Most importantly, outside of very specific events, the three of them do not usually cooperate with one another. As such, they constantly switch who you are synced with as if they were jockeying for who gets to be on point.
The Emblem of Bonds uses Chrom and Robin, but unlike the two Emblems above, their paths do not divert. In fact this references Awakening's Pair Up system in the most literal sense. Chrom may be the main unit, but Robin is right by his side ready to support him.
While Firine, Brodia and Elusia designate parts of their castles specifically for their primary Emblem Rings, all Solm gives to theirs is a "doo-dad drawer". This is Played for Laughs, but unlike Celica, Roy and Lyn, who were all of royal descent, Ike is not and never would become royalty. In fact, Ike in his home game hated the nobility and only took on a noble title at all to help his client, Elincia (and promptly renounced it as soon as the job was done), so the Solmese royals treating him so haphazardly compared to the others would be just the way he'd like it.
Pale Sands is not merely a name-dropped nation to explain Kagetsu's Japanese-theming; there is indeed a portion of the world map in northeast Solm that has paler colors than the rest of it and that your party never visits due to no missions taking place there.
The Joke Weapons obtained from the Ancient Well are all sweets. Rafal, who's from the Alternate Elyos on the other side of the Ancient Well, has a Sweet Tooth and makes sweets himself. Additionally, one of his Ally Notebook pictures depicts him eating downsized versions of all of these weapons (except for the Croissbow). It's not much of a stretch, then, for those joke weapons to be his idea and creation.
The Rings, when you get them, are generally powerful. It's actually an aversion of the usual Sacred Weapons - in most Fire Emblem games, a sacred weapon is simply Too Awesome to Use until the final chapter. The only games where they did see casual use were in the games where they were unbreakable or could be repaired.
Hector's Runesword, a Spell Blade, calculates using 50% of the user's Str instead of Mag like in the GBA games, including his home game The Blazing Blade. Although a Guide Dang It! moment since nowhere it states this in-game, there is a major hint that it does it this way: why does Hector, a physically strong yet Magically Inept Fighter, wield a Spell Blade if it doesn't benefit him the best if it does the normal calculation?
Alear’s dream in the beginning of the game involving the Royals and Emblems later met in the game makes a whole lot more sense when it’s revealed their past self had encountered them shortly after they travelled into the past. Doubly so that they’re depicted as their blue and red self in the dream as past Alear also saw their future self, whom is what they would wish to become.
Nemesis is the "Dark Emblem" that represents the final boss of Fire Emblem: Three Houses because he's the only Final Boss that could be considered genuinely "Evil" ''regardless of the route.
While the game doesn't really explore it, being an Emblem could reasonably be quite the source of existential horror. Most Emblems seem to on some level understand what they are and are quite comfortable with it, even if they still often find themselves speaking as if they really lived the life of the person whose memories they share. However, some Emblems (such as Emblem Veronica) appear to genuinely believe they are that person and don't seem to understand that not only is their original likely long dead from old age, but they have no viable way to access the home world they remember so vividly (as while putting a Emblem into dormancy is a means to allow them to survive such a journey, opening portals to other worlds is both dangerous and difficult). Others appear to not understand/remember their limitations as Emblems, such as Emblem Camilla repeatedly forgetting that she has no need to bathe and is unable to do so regardless. While this is more humorous than horrifying, it does seem to indicate there is a certain mental dissonance Emblems can suffer from.
When Engaged to the Emblem of Rivals, your units have a chance to say "that's [x] for ya!", usually filling in [x] with either Golden Deer (if Engaged to Alear), or from each royal's respective nation (Firene for Alfred, Brodia for Alcryst, and so on). Veyle does this too, but instead of naming any place, she hesitates and says "that's... me, for ya!". She probably would have said Gradlon, except nothing about Gradlon and her upbringing there was anything pleasant to look back on.
Usually when Corrupted die, their bodies dissolve away. That Alear and company were avoiding killing anyone who looked human can explain how they were able to go so long in the Xenologue without noticing that basically the whole population was Corrupted, but then why didn't they notice when Nel in her transformed state kills the alternate Ivy and Timerra right in front of Alear? Then we get an implied answer (assuming he was being serious) from alternate Fogado in the next battle. Nel didn't kill Ivy and Timerra with claws or flames, she ate them whole. There were no bodies visible to see dissolve.
The Wolves and Ice Dragons of the Divine Paralogues are Palette-swaps of their Corrupted variants in the Fell Xenologue. These are also Fabrications, created by the Emblems themselves. So the question is, are the Emblems so traumatized by what happened in the Alternate Elyos that they can't imagine regular Wolves and Dragons anymore?
Near the end of the Fell Xenologue, it's revealed that Nel, Rafal and the Four Winds are the only non-Corrupted beings left on their version of Elyos. We know the royals (and likely their respective armies) died in the same war that took the lives of their parents - but just what the hell killed everyone else?!
Due to the fact that most people in the Alternate Elyos is the opposite of the version in normal Elyos, one has to wonder how characters that don't make an appearance nor get mentioned at all like Yunaka, Jean, Seadall and Anna were in this world:
Yunaka probably got the opposite face-turn: she grew as a gentle girl and then turned into a cold-blooded assassin, eventually dying by the hands of her master or executed for her crimes;
Jean probably hated his parents and didn't want to become a doctor, and without a Divine Dragon to save him, he and the rest of the village where he lived were likely killed by the Corrupted or bandits;
Seadall probably suffered a similar fate, with him being killed by the Corrupted or bandits in the fortress;
Anna would probably have been a poor girl without a family and a home to return to, and she likely was killed by the bandits seen in the Paralogue where you recruit her.
Lindon probably died in an experiment - which is a mercy in this world.
Judging by the special dialogue you would get if she fights against Ivy, Lindon and Hortensia, it's not too hard to believe that Alternate Ivy hates Alternate Hortensia so much that she forced her to wear a cute, showy outfit just to degrade her further, making her more and more depressed.
If Alternate Hyacinth really did survive the war and wasn't just another Corrupted, then he outlived not only his daughters, but every other ruler on Elyos. That must have been rough on his psyche.
Revisiting Alternate Elyos, and doing a skirmish there, will reveal that you're actually in an Alternate Universe version of the place. It could be an Alternate Timeline or merely the Alternate Elyos in the past, but it's certainly not the exact time and place the Four Winds or the Fell Twins left. How screwed is this setting? Well, doing a Skirmish in the Bracelet Altar (Xenologue 1) will have Rafal remark that maybe the Rafal of this world hasn't made the samemistakes... while in Firene Gardens (Xenologue 2), he'll say that he has the power to "wipe this place clean", but that it "would have little meaning"...
The characters taking this viewpoint makes extra sense when one considers that after the thousand years Rafal spent with Nel alone in Alternate Elyos, there should have been no Corrupted left to fight (as Corrupted have quite limited lifespans and cannot be raised again if this lifespan runs out).
