The story of the game would unite all the heroes of Fire Emblem from Shadow Dragon to Awakening, encountering heroes from the first Final Fantasy up to XIII, which they start fighting, and then the villains of both series would join forces to defeat our heroes. Leading the heroes of Fire Emblem is Marth, and leading FF heroes is the Warrior of Light of course, for the villains, the leaders are Medeus and Garland.
The gameplay could have the same concept of Dissidia, except that is Final Fantasy and Fire Emblem combined. Each would have their Criticals and EX Burst. And players can get to play as their favorite heroes or villains from both factions. It would be difficult since main games of the Final Fantasy series have been on the PlayStation since FF7, it would be great if heroes of FF would be seen in Nintendo, of course, Final Fantasy started in Nintendo from FF1 to FF3, then from FF4 to FF6 it was in the SNES, when FF7 came out up until 12, it was usually a PS exclusive, and then going multiple consoles when FF13 came out.
In terms of a final boss, they would fight against Chaos of course, and then Feral Chaos. FF characters would find their crystals, while Fire Emblem heroes find their legendary weapons. Since there have been so many crossover fighting games like Marvel vs Capcom, Tatsunoko vs Capcom, Street Fighter X Tekken, Mortal Kombat vs DC, and coming soon SMT X Fire Emblem, I believe that there should be a crossover of Fire Emblem and Final Fantasy. Why? Because both franchises are a hit in Nintendo and Sony, the stories are well written that gives you an emotion that you're in the game with the characters, music themes are epic, and funny moments as well.
What do you think? Should Fire Emblem have a crossover with Final Fantasy? You decide!
God Bless and Play Hard Gamers!