Fairy tail, Laxus little sister

This is about Laxus little sister, Marceline (kinda from Adventure time), who neither Laxus or Makarov knew existed. But one day at the Guild the citesents of Magnolia tells the Guild that a scary monster has moved in to a caven in the forest, which only children have seen, and that they all need to go and make it go away or kill it they don't care. Then as the story goes on they will learn the truth, when they meet Laxus dad at the battlefield when he comes for Marceline.
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hope you don't mind my english! It's not my first language. I don't own any characters from fairy tail or Adventure time.
This is my first story, hope you like it!