A Brief Storyline

So here's what I turned in to my class.  It's kind of rough.  I need a reason for the two girls to dislike each other, but I'm not sure I like what I have.  I'm also not sure if I like the name "Ettie".  I was looking up Victorian names and Ettie is short for Henrietta.  I used it, because it's different.  My second choice was Natalie.  Anyone have any ideas?

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A Brief Storyline:

Claire and Ettie are two normal 15 year old girls.  At first they are good friends, but an accident during their chemistry class' final lab ends their friendship.  Both girls blame each other for failing the class, but neither one will admit that it was both of their faults.  They eventually become rivals, who can't stand the sight of each other.  One night while sleeping, they find themselves stranded in a dreamworld full of puppets.  Rather than working together, they decide to split up and figure out how to get home by themselves.  

Claire finds herself in the whimsical world inhabited by the Shiriennes, a race of colorful puppet-like creatures.  Their home is drenched with bright colors and is full of clouds and stars.  

Ettie ends up in the dark ethereal world inhabited by the Kuriole.  The Kuriole are quite similar to the Shiriennes, but instead of being brightly colored, they are darker and more gothic in appearance. 

The Shiriennes and the Kuriole are both descended from a common ancestor, but are at war, because they both believe that the other wants to take over their home.  There is a prophesy passed down through the two clans stating that an outsider would come and lead the clan to a victory in the war.  So the Shiriennes ask Claire to lead them and Ettie is asked by the Kuriole to lead them.  Both oblige.  

The girls must travel through their respective worlds, recruiting Shiriennes and Kuriole to aid them.  Each creature has a single power, some stronger than others.  It is up to the girls to gather the strongest, so that they can defeat the other side.  

What the Shiriennes and Kuriole don't know, is that a common enemy is inciting their hatred.  Loki a trickster and his only wish is to cause chaos between the two sides.  In the end, the two sides must overcome their differences and unite to face their common enemy.