Isn’t that just Fire Emblem Online/FEO?
I’ll link that thread here so you can see what I’m talking about - Fire Emblem Online - A Sheets-based FE TTRPG
I hope I’m not coming across as mean 
I just wanted to point you to something that could be of interest related to this topic; if FEO doesn’t fit what you’re describing, then I’m not sure what that would look like, but I’m sure other members can enlighten the both of us in this thread 