Oh God..
Wait never mind, I forgot how much of a jerk YHWH is.
How I think it will work.
1) You get characters from both SMT and FE, and they are fighting because
the FE people want to stop the war, but the SMT people want the freedom
to choose what path they follow.
2) The game is a dungeon crawler, and every time a battle happens you have
to set up a formation and everything. Think devil survivor, or fire emblem.
3) You can recruit demons and evolve them with master seals/
4) A superboss will be lucifer paired up with satan.
5) Permadeath