Hopefully not. I like Pokemon and everything, was my first game from gba (emerald), but you can't combine Pokemon with Fire emblem Heroes. Is like saying, I like peanut butter and I like cereals, and I combine them for breakfast. Disgusting. (Nah I found my cereals).
Why not ? The logic is pretty similar :
You begin with 3 starters, Red (Alfonse/Charmander), Blue (Sharenna/Squirtle) and Green (Anna/Bulbasaur)...
And Red > Blue > Green > Red
Wait just a dang-gone-ghost-eatin-minute. Pokemon x Fire Emblem Heroes sounds weird, but I can also see it happen. I'm actually curious how it will work if it does happen.
Pokemon GO
Fire Emblem Heroes
Fate Grand Order
Dragonball Legends
Dragalia Lost
IV Calc
Heroes