Hawk: Okay, this is technically breaking site guidelines, but a lot of the terminology might not make sense to everyone, and if everything goes according to Keikaku, this will come out on the same day as the real chapter 1 (well, prologue). That, and I'm attempting to make this as close as I can to a real Fire Emblem game. So I guess this could be seen as a sort of "Tutorial", this is mainly gonna be about the classes of the characters, the new "features" and the main themes and inspirations behind this.

Just something to be aware of, this is not me saying this will be the next main-series game. If an FE game comes out and is similar to this story, know that the whole thing is just a coincidence (One I'd be happy with, though). So without further ado, let's get into this.

Classes:
Kinda similarly to most games in the series not called Gaiden, Sacred Stones, Awakening, Fates or Echoes, there are no split promotions in Blazing Flag, but 3rd Tier units exist in their stead, as do converging promotions.
To list them off:

Lord → Captain → ?

Myrmidon → Swordmaster → Trueblade

Soldier → Pikeman → Halberdier

Fighter → Barbarian → Berserker

Archer → Sniper → Marksman

Thief → Rogue → Assassin

Gunslinger → Rifleman → Duellist

Mage → Sage → Scholar

Monk → Bishop → Saint

Arcanist → Sorcerer → Diabolist

Cleric → Troubadour → Valkyrie

Sword Armour (Knight) → Sentinel → Dreadnought

Lance Armour (Knight) → General → Dreadnought

Axe Armour (Knight) → General → Dreadnought

Bow Armour (Knight) → Sentinel → Dreadnought

Sword Knight (Cavalier) → Gold Knight → Great Knight

Lance Knight (Cavalier) → Silver Knight → Great Knight

Axe Knight (Cavalier) → Gold Knight→ Great Knight

Bow Knight (Cavalier) → Silver Knight → Great Knight

Musketeer → Dragoon → Conquistador

Mage Knight → Dark Knight → Wizard

Pegasus Knight → Falcon Knight → Seraph Knight

Wyvern Knight → Wyvern Lord → Dragon Master

Griffon Knight → Griffon Warden → Griffon Sentry

Manakete

Bard

Dancer

I tried to balance classes from Awakening/Fates, the older games (particularly the Tellius games) and some new ones. There are a few more than this, but the ones that are missing are surprises.

You may have noticed a new weapon type among the others: Guns. They're a lot like bows in a way, having a range of 2, but without the effectiveness against fliers. As a trade off however, they're more powerful than any other weapon type. They also interact with the weapon triangle in a unique way, when at 2-Range they gain advantage over Swords, Lances AND Axes. However at 1-Range, they're weak to those weapons. To give you all the weapon types, there are: Swords, Lances, Axes, Bows, Guns, Knives, Light Magic, Dark Magic, Anima Magic Staves, and Dragonstones. Also unlike Gaiden & Fates, weapons break in this entry. As for the Weapon Triangle, I'd say the GBA games had a decent triangle. So I'd use that version of it.

New mechanics added here are the "Fleet" and "Helm" mechanics. The Main Lord Anton has in his possession a rare build of ship, but that's not the only ship he can have. After defeating enemies in skirmishes, you're given 2 choices: Sink the ship and get gold from the bounty on the captain's head, or take the ship for yourself and add it to your fleet. You can have up to 3 ships in your fleet at any given time, with 5 back-ups. A ship is like a platform that can be moved and rotated by a unit if they're at the ship's helm, however it will use up their turn. Using that, a unit is able to move the ship around any ocean tiles on the map, although how far the ship can move depends on the wind and where it's blowing.

Ships, much like units, have stats, and are also able to level up and gain weapon ranks, which in their case, is Cannons.
There are 4 types of ships:

Flagship: you only get one of them, and if it's destroyed, it's Game Over.

Frigate: A lot of Defense and Resistance, but slow as hell.

Freighter: Speedy, but little in the way of Strength.

Galleon: A Glass Cannon. Low Defense, but high Strength

Ships can also be upgraded with Sails to increase movement, Cannons to increase strength and Plating to upgrade defenses. And with the exception of the Flagship (which you will get the name to soon), any ship can be renamed and have its flag customised. However, the Flagship has another layer of customisation: much like My Castle from Fates, the Flagship acts as a base of sorts between battles where you can do things such as view supports, get furniture and watch prior cutscenes.

You can dock in port towns to restock on supplies and weapons, as well as forge weapons to improve them, visit a fortune-teller to summon Einherjar (heroes from past Fire Emblem games such as Marth, Lyn, Chrom etc.), upgrade your ships and visit a tavern to hear rumors (how to access paralogues).

Skills will be making a return here, as will Personal Skills. Those were one of the few things I actually liked about Fates. Supports will be back, but very few characters can achieve S - Support with each other. Similar to Valentia, the Pillar of Modern Warfare that is Pair-Up won't be present in this story. It's just too hard to balance correctly.

Some major inspirations for this are Red Dead Redemption, in the way it's about a man in a world in which he no longer has any place. Final Fantasy XV, due to its fantasy world not in a Medieval Europe-Fantasy, but set in a different level of technology. A discarded concept for Awakening that it would be set in the modern day, and even on Mars at one point (I see what you did there, Intelligent Systems ( ͡° ͜ʖ ͡°)). And of course, The Golden Age of Piracy from the 1650's to the 1720's. I also have to thank those who've made Fire Emblem mods for Civilization V: Brave New World for making me think of this question.

Just something to keep in mind, there exist 2 continents in Blazing Flag with 8 territories between them. To list off the ones you need to know:

Continent of Aegea

Empire of Castellon

Empire of Varese

Empire of Hevale

Holy Empire of Anatahr

Kingdom of Tsukimoto

Aurum Island

The Castellonian Sea

Pirate Kingdom of Barbarosia

Continent of Arbsol

Empire of Yuar

With all that out of the way, Welcome, me mateys, to Fire Emblem: Blazing Flag.