Lucy, princess of the celestial world. One of the most strongest keys to exist, surpassing her father and mother. Yukino is the holder of that key, though not strong enough to summon her. Lucy forces through the gate and becomes friends with sabertooth. She has a secret though, she is in love. With who though? who has the heart of the brightest member of all? What if someone doesn't like this love? Guess you'll just have to read.
(The author of fairy tail wrote fariy tail, I have simply wrote a different plot line.)