What the Story is About in Final Fantasy XIII Versus

Noctis and Stella fighting each other for the power of the crystal, are they enemies or lovers?, Noctis is the last survivor of his race, his role is to protect the crystal in the temple that he lives in and hand it to no one no matter what, Stella needs the power of the crystal because her kingdom needs power to survive in a time of war

Will stella abandon her kingdom for noctis? is it fair to betray your entire nation that trusted you for a friend or a lover? it seems both of them put their emotions a side when it comes to the "Crystal", Noctis will protect it no matter what and stella want it for her kingdom no matter what (That's why they are fighting emotionless in the trailer), yet there is a third person who wants the crystal too!

An army is useless against those who wield the power of the crystal, only Noctis and Stella can absorb the power of the crystal and that's why Stella nation sent stella to retrieve the crystal from Noctis Temple, will she able to do so? that's what we are going to learn in FF Versus 13 Story