As a long-time Fire Emblem fan, I really enjoyed this game. Usually I don't play rougelikes, but this combination is very promising. The levels were well balanced to be challenging, but they never felt unfair. Leveling up characters and collecting better equipment was satisfying, as it should be.
The UI could use some improvements. It would be nice if you could just hover over a unit to see the relevant info about it instead of having to click on each of them. Also, the consumable items should have a description of what they do and whether an effect is permanent or just for one battle.
There have been a few very annoying bugs, mostly after loading a save file. Most or all of my units got deleted, or I couldn't control them anymore. This happened both, in the browser and the downloaded version. Even so, I played through all three campaigns.
All in all, I had a lot of fun with your game and hope you'll keep working on it.