Mages in Valentia cast magic using their own life force... but in Archanea, they don't. Why not? Well, the Early Installment Weirdness can be easily justified by the fact that magic was learned from a different source - Gotoh in Archanea, but probably Duma in Valentia. Easily the technology (or the method) that Gotoh created (and taught) in Archanea didn't make its way to Valentia yet so they were doing it the old fashioned way. This is also why, when you fight Valmese forces in Awakening, they use tomes and staves because at some point, the method to cast magic without using your own health made it there.
So, if a mage from Archanea came to Valentia, would they Cast From HP? Actually, we don't know — the characters from Archanea (Zeke and the pegasus sisters) are fighters not mages.
Adding onto this further is the fact that if you go through the efforts to reclass either the sisters or Zeke into a magic using class, they still Cast From HP. Why? They learn the Valentian method.
This also explains why units do not use books or staves when they break they'll Cast From HP. Or maybe, they actually don't know HOW to cast from HP!
In Act 2, Celica has a dream where Alm fights Rudolf and gets killed. This contradicts Rudolf's original plan to have Alm and co. defeat him and gain the power to fight the Duma Faithful and is therefore out of character, but it makes sense as Celica sees this dream via the Mila's Turnwheel. She is not seeing what will be the future, she is seeing an Alternate Timeline where she did not leave the monastery at the same time Alm left Ram Village. Therefore she was not around, and as a result of the Butterfly Effect, Zofia is now under Rigelian control, Celica somehow got captured or killed by Rudolf, Alm's friends are dead, and he is left to fight Rudolf alone (and, judging by his aura, by this point Rudolf had apparently been corrupted by Duma). Her merely deciding to leave changed everything for the better.
Why does Fatigue not kick in between regular battles? Actually, it makes sense your characters had ample time to rest and eat up in between battles.
Whereas most other battles are Rout maps, Rudolf's is a Defeat Boss map. Odd choice... but wait. The Decapitated Army is totally justified here. Rudolf ordered anyone left to surrender if he fell. The battle ends because anyone still left standing on the Rigelian side surrendered.
Additionally, Rudolf had another reason for forbidding Berkut from joining the battle. While he only told him it was because You Have Failed Me, it was also a Thanatos Gambit. Berkut survived his previous encounters with Alm because Berkut knows when he's outmatched... but this would have been his last stand, ergo Berkut would fight to the death and refuse to surrender despite orders, either getting himself or worse, Alm, killed. Adding onto this, Berkut is the crown prince of Rigel as the only eligible heir or so he thinks. Thus, forbidding Berkut from joining the battle would mean (to the others not in the know) there is still an eligible heir if Rudolf dies. And tying this off, Berkut would easily ruin Rudolf's plans if Rudolf had to explain.
So, the area of Valm that Say'ri, Yen'fay, Cherche, and Virion come from is the south... and they have French accents. The south is Zofia, where the residents are historically lazy and decadent. Very funny, 8-4.
If the Mila Tree is what grew on Mila's remains like how the Demon's Ingle may have grown on Duma's remains, why such a large tree? Of course! Mila is the Earth Mother after all. And both the Mila Tree and Demon's Ingle are Duma and Mila's tombstones. In a way, it's kind of representative of what they stood for.
Not only that, but Duma helped re-fertilize the Valentian soil that was becoming barren volcanic soil is highly fertile, after all.
Regardless of what you thought of Rudolf's decision to start war to draw out the Brand-bearers, what with the dragons and all of Valentia being at stake, he just resorted to the ultimate logical conclusion of Duma's core philosophy. Misery Builds Character, and if War Is Hell...
Why does that Brutal Bonus Level not have a Mila Shrine in it to get rid of fatigue? Because it predates worship (or acknowledgement) of her in Archanea! Belief in her did not exist at the time that Thabes was a thriving city and eventually sealed.
While there is a Mila idol in the port just outside of Thabes, it could easily be explained that Mila was just starting to get known in Archanea at the time of Echoes. And while a few NPCs mention that looters go into Thabes sometimes, they probably don't go in past the first couple floors, and if they're not staying long, then they'd see no point in stopping to put a Mila shrine in there.
Why do almost all Witches operate on an A.I. Roulette, potentially resulting in them teleporting to attack someone right next to them and/or picking a fight with someone who'll mop the floor with them? Their souls belong to Duma, who is insane. The unpredictable nature of their movements and attacks are a result of Duma's insanity.
Barons use a Sparta Kick as a counterattack in their battle animations. Naturally, they overclass into Spartans.
Celica's starting class is Priestess, which would be a promoted female Mage, but Celica starts with this class, as opposed to any other main character, who would have an exclusive class, like Alm's Fighter class. This is, of course, a disguise, as Celica would be able to pass as a Priestess if anyone would normally see her. She does take her role as Princess Anthiese once again and is promoted from Priestess to Princess.
Echoes introduces Conrad, a knight who wears a mask over his eyes. Now we know where Camus/Zeke/Sirius got that idea from.
Mila's dragon form (seen in a sealed stone state) looks oddly disfigured and "ugly" compared to the beautiful/magnificent dragons seen in many other Fire Emblem games. But not only does this give her a physical link to her brother's dragon form, the disfigurement further implies she was suffering degeneration like her brother.
On a related note... if Mila is starting to degenerate like Duma, then it seems confusing that the Duma Faithful all look so weird while Mila's followers look more normal. First off, the Duma Faithful also make sacrifices to Duma, implying that without tapping directly into the gods' powers, the followers wouldn't degenerate too. However, one could also assume that Mila's degeneration started more recently than Duma's, so it wouldn't have had as much time to spread.
Berkut is the third major character in the series to be directly empowered by a divine or nearly-divine entity. The first guy to get divine power, Ike, is completely heroic in both thought and deed, as is the deity that empowers him. Naturally, he gets the player's color, blue, for his Battle Aura. The second guy, Takumi, means well enough, but his personality is increasingly subsumed by the malevolent deity's will, to the point where there is nothing left of him by the time you fight him for the last time. He gets purple, a mix of blue and red. Berkut, on the other hand, while somewhat tragic, freely makes the decision to enter a pact with his malevolent deity for his own selfish gain. He gets the enemy's red for his aura.
Alm and Celica both perfectly represent the positive traits that both Mila and Duma spoke of in the Memory Prism flashback, even though they both also firmly represent one nation in terms of their origins.
Alm's journey involves facing the realities of war and becoming stronger through hardship, which was what Duma felt made mankind stronger. However, Alm never gives up his empathy for others, nor does he forsake friends or loved ones for his own gain, and his motivation is to end war over gaining power. Basically Alm ends up showing the Might Makes Right qualities that Duma advocates for, but without the superiority complex or obsession with power that made Rigel the problem it did by rejecting the chance for power for the sake of others.
Celica firmly believes in peace and strives to bring prosperity to others, so that others can live their lives happily. However, Celica also is aware that she needs to fight for her beliefs, and won't tolerate injustice towards others, while also having gone through a life of hardships due to being forced to hide her true identity. She essentially takes Mila's teachings of peace, but funnels it through the lens of someone who has endured hardship like how Duma believes man should, thus instead of letting peace come to her, Celica fights to bring peace to others instead.
Nowi was a divisive character because she appeared to Retcon Tiki's Last of Her Kind status, but you can see in Echoes that Mila's hair is the same color as Nowi's. Add into the fact that Nowi was born "across the ocean and way to the left," which is exactly where Valm is... It would appear Naga's not the only dragon who has descendants.
The one spell that you do NOT cast from HP? Nosferatu life drain. Wait a minute, Nergal harvested quintessence from others... Oh, Crap!. Our clerics harvest quintessence! Similarly, that also means that Canas is as well Bad Powers, Good People?
Canas himself, despite insisting that Dark Is Not Evil, also acknowledges the danger inherent in Dark magic (which Nosferatu is in that game). And since Nosferatu has always been life drain, regardless of what "type" of magic it is considered... yeah. Even if we assume that quintessence is unique (or at least, more known) in the Elibe games, there's very little "fridge" and more "all but stated" to be Bad Powers, Good People at play. Though there is some creepiness over the fact that it's a Cleric spell of all things here...
The Demon's Ingle was known as such to avoid Continuity Lockout in the localization of Awakening, but in Japanese it's called Duma's Remains. While the location did not match up, Echoes explains that that's where Duma was buried. It's not visited specifically in Echoes, but that does mean that Duma's presence might have turned it into a volcano... Additionally, the localization changing that area's name while keeping the Mila Tree implies that Duma was either forgotten by history or continued to be demonized.
Consider this: Rigel was the more stern and militant nation, and, thanks to Jumping Off the Slippery Slope, they became known as bloodthirsty and violent. That makes the idea of Duma's Remains eventually becoming known as "The Demon's Ingle" because of Duma getting continually demonized very plausible.
Apparently, Mila and Duma are both succumbing to the madness that set the stage for Fire Emblem 1's backstory with Medeus. Yikes, just what would have happened with Mila?! Considering the Slasher Smile she gives Rudolf when he confronts her, it's probably already happening by the time the game begins.
Considering that Mila had already turned into a majorLazy Bum, causing Zofia to start becoming barren, and most Zofians to become major hedonists... yeah. She'd range from severely neglectful at absolute best, to attacking (or even killing) anyone who so much as complained to her about the situation, or who even knows what else. Heck, Desaix is proven absolutely right when he assumes that Mila won't step in to save the royal family. Mila's definitely started going mad by the start of the story.
Silque, Tatiana, Halcyon, Specters, and an NPC in Sage's Hamlet reveal in different ways that the Duma Faithful once had Sages, Clerics, and very likely Priestesses in their ranks. Yet now only Witches and Arcanists/Cantors are the only magic users remaining. Combined with how even daughters are sacrificed, it seems pretty clear now why Silque's mother left her in Zofiaaway from the Faithful.
After Nuibaba is defeated in Echoes, a cute-looking cleric of the Rigelian church says that she (Nuibaba) gathered "young and comely" (read: pretty) girls to sacrifice them and keep herself young and alive. At the same time, Alm can free Tatiana from a cellar there, and it's later revealed that Nuibaba kidnapped her so Jerome could force her lover Zeke to fight the Deliverance. Plus, if the player encounters Zeke in the Planes of Rigel before fighting Nuibaba, neither him nor Tatiana can be recruited. This means that, if such a thing happens... poor Tatiana may not just be Killed Off for Real, but she and probably the aforementioned cleric (and maybe another girl who's seen as an NPC) might be turned into human sacrifices by Nuibaba since they fit in the "standard" that the cleric mentioned. Ouch.
It's even worse than that. Since Tatiana is already (at least strongly implied to be) dead by the time the party gets there, it's hard to tell when, exactly, she would've died. This means that they may have been planning on killing her off anyway, even though Zeke never defected in that situation, making the whole thing into a "Shaggy Dog" Story. (Not helping is the fact that if you even enter Zeke's map and then save, you've doomed Tatiana, even if you exit and go back to the world map. Ouch, indeed.)
Echoes-only: Why is it that in her artwork and the cutscene where she fights Alm, Celica is depicted with the Ladyblade instead of the Beloved Zofia, her personal weapon and what should be her counterpart to Alm's Royal Sword or Falchion? Firstly, the Beloved Zofia is locked to Celica, not just any bloke with royal blood, and it's not really Celica dueling Alm to the death there. Second, take a look at the Ladyblade: magic-oriented arts, and is twice as strong in the hands of female units. It being found in Duma Tower looks like a classic case of a game saving the best equipment for last, but other than Priestesses of which Rigel apparently has none left, there's some suspicious synergy between the Ladyblade as a weapon and the magically-empowered Witches that are created in the very dungeon they placed it in. If only a sword-wielding Witch would come around...
Echoes only: Knowing Rudolf wanted to be killed by his son's hand rather than the Duma Faithful's, was he intentionally sending people out to face Alm who he knew would either surrender or die fighting? Yikes! Apparently Rudolf was cleaning up Rigel for the One Kingdom.
Among these is Berkut. Was Rudolf intentionally trying to off him? Yikes! Berkut is still family! At the very least, this may be alleviated by assuming Berkut was acting by himself, and Rudolf never called him back because he knows Berkut Knows When to Fold 'Em.
Further along with Berkut... he is basically a "Well Done, Son!" Guy. But one reason for this could be the fact that Rudolf knew Alm was still alive... hence there was no need to treat Berkut like a son. Good going Rudolf! You screwed up your nephew by keeping him Locked Out of the Loop!
Walhart's methods and beliefs were very akin to Rigel before it got cleaned up, suggesting that at some point the real lesson of Alm and Celica's deeds were lost to history, leaving only the story about Alm slaying gods and conquering the continent (which would also explain Walhart's Nay-Theist beliefs) It's telling that in Heroes, he shares the same weapon effect with Brave Alm.