We need to get Claude in there to slap Vice President of Racism Shinon around.
Fire Emblem: Blazing Blade (aka Fire Emblem): Eliwood and Hector
Why both of them are here: Lyn took the main slot for Blazing Blade as the most popular character in the game (and the first lord the West ever had), but there were still two other lords to work with and based on the Three Houses precedent, we include both of them.
What they could do: Eliwood is associated with the sword and Hector the axe, so an “Omnibreak” effect - literally giving the ability to break any sword, lance, or axe unit to the wielder once during a battle.
Other possibilities: Either the obligatory wise man in Athos, or the refresher duo of Nils and Ninian - but these seem to be remote possibilities.
Fire Emblem: The Sacred Stones: Myrrh
Why they’re here: Sacred Stones has twin protagonists, but since Eirika can swap over to Ephraim anyway we have an open slot for someone from the world of Magvel. Myrrh, the game’s obligatory dragon, would probably end up getting first crack at the spot since we actually don’t have a Tiki archetype beyond the OG anyway.
What they could do: To borrow a trick from Heroes, where all dragonstones deal “adaptive damage” (or damage based on the lower of the enemy’s Defense or Resistance stat) on ranged opponents, the person with Myrrh equipped gains innate adaptive damage on EVERYTHING.
Other possibilities: Seth is the most busted character in Sacred Stones runs, but if not Myrrh the slot would likely go to one of the other big 4 royals of the game: Joshua, Tana, Innes, or L’Arachel.
Fire Emblem: Path of Radiance: Soren
Why they’re here: A lot of the plot of Path of Radiance is about the conflict between humans and the laguz - and without spoiling things, Soren is the epitome of that conflict. He’s also one of the few people Ike actually bothers to fight for. And since the role of magic user in Tellius was given up by Micaiah in favor of healing, we have an open spot for one good Tellius mage.
What they could do: Mass (if not full screen) Res debuffs for everybody - and allies in a certain range get the ability to double these debuffs since Soren was the main tactician of PoR.
Other possibilities: Normally we’d pick Ike’s father Greil, but Ike already swiped his trademark axe. As tempting as it is to get the main female member of Greil’s Mercenaries (Titania), really this slot would probably go to that famous Smash assist trophy and quality social media manager Black Knight. If they didn’t use him for Radiant Dawn, but more on that later.
Fire Emblem: Radiant Dawn: Sothe
Why they’re here: In continuing the trend of people related to Ike being represented, here’s his baby mama.
Actual answer; Sothe is the second best member of the Dawn Brigade, who are most of the original characters to Radiant Dawn, and I mainly have him here for his in-game effect since I don’t recall it being in a Fire Emblem before.
What they could do: The wearer of Sothe’s ring would get what Final Fantasy calls a “Mug” attack; the ability to steal an item from the defending unit when initiating combat. There’s been major defense debuffs on thieves (mostly in the form of Sophie from Fates, who could disrobe people on contact), but how about swiping their shield or elixir entirely?
Other possibilities: Any trademark Laguz (Caineghis, Dheginsea, Nailah, Leanne), empress Sanaki of Bengion… or you could throw a PoR unit in as well. Heck, the Black Knight might be better suited as a Radiant Dawn rep since you can actually play as them for a time in RD.