So as we know the Almire people were led by Vanaduke, as reward for beating Darkfire Vanaduke you are awarded the crafting material for the Almirian Crusader Armour
you can also create a Crest of Almire Shield from the blackened crest which is the reward for killing Vanaduke and gathering the tokens

We have the helmet, armour and shield of the Almire, what weapon did they wield though?

So, why not have another expansion mission or another mission set or a piece of weaponry?
the mission will uncover more of the lore surrounding the Almire, who were they and how did they live?

at the end you will be given a material for crafting a 5* weapon that the Almire used, you will make it with the 4* Calibur or Flourish and it will deal Pierce or Shadow damage
Another way you can create this is creating a 4* Spear that looks like the one the Crusaders and the Deadnaughts use, firey and cracked up similar to the blackened crest, then create a "purified" version in a similar fashion to the Crest of Almire

As for the idea of a Gun or a Bomb, I don't rely think one would work with the Almire but I think a Crossbow style weapon for a gun would work, this would also make the mission more interesting having Almire Knights as Turrets that fire upon you similar to the current turrets.

"but how can we fight an extinct race?" I hear you ask, well I was thinking; what if when studying the Citadel Ruins we uncover a Library, within we find books containing souls of the Almire Crusaders who reveal more about there kingdom and what led to there once beautiful land being turned into hell incarnate, then we find another book but this one contains an ancient spell which pulls the knights back in time where they fight there way through the streets of Almire and into the keep, here we fight King Vanaduke but before you land a finishing blow he escapes, abandoning his people behind. after that you go down an elevator and speak to more knights of almire and get the material for crafting there weaponry and can use a special "Anvil of Almire" to craft them.
after that you will go to a portal to return but before that you see flames approaching in the distance then awake in the Med bay part of the Lab where its revealed they found you passed out the owlite keep.

make changes as you would, but you cannot deny it would be pretty ace to find out more about what caused Firestorm Citadel to become this way