Final Fantasy xiii

Elllooooo people =]
Okay I consider myself a nerd.
All you other nerds out there.
Haha no I'm kidding nobody is a nerd.
Um haha anyways can you guys help me.
I don't understand, what is the difference between Final Fantasy xiii and Final Fantasy versus xiii?
I don't get it AT ALL.
I know Lightning is in Final Fantasy xiii and Noctis is in the other, but I don't get the difference between the two of them.
I am soooooo stupid.
I am kind of a newcomer for the movies, slash game, sooooo hear me out. haha
Haha thanks guys.
YOU GUYS ARE AMAZING =]
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