>>> For the world something similar to FF12.

Main character: A bad ass amazon-like warrior princess which is actually a guy raised as a girl. She/he would look like Fang from FF13 but maybe with bigger breasts..

Love story: the main character is forced to marry another princess (a girl) from a far away kingdom but our main character is actually in love with a low rank soldier (another guy) from the kingdom.
The kingdom`s royal marriage gets interrupted with the invasion of a super powerful army of Dark Knights from hell (or something).
After an intense battle the kingdom gets completely obliterated and our main character manage to escape with his lover (the low rank soldier) and then their journey begins..

Thats pretty much all I got so far.

Hey SE, you are totally free use my super awesome FF idea for the next FF game.. The success is guaranteed!.