Gate Holder of the Celtic Zodiac Keys, and also Natsu's younger sister?

(GrayxOC) Natsu Dragneel has been, well sort of, keeping a secret from everyone. He has a younger sister! The 18 year old has a 17 year old younger sister! Yuki Fuyu Dragneel! Yuki and Natsu grew up together for as long as they can remember, since they can't remember their actual parents. Yuki learned dragon slayer magic also, but not from Igneel, but from Tsuki, Igneel's mate. Tsuki is the Galaxy or Cosmo Dragon slayer, but, Yuki doesn't know any destructive magic from Tsuki, so Tsuki also taught her Celestial keys magic. In 777 when the Dragon's disappeared, Natsu and Yuki both were very sad and distraught. Natsu decided they would explore to look for their dragons and after a few months of exploring, Yuki disappeared from her older brother. Natsu was founded Fairytail's Master the day after her disappearance and has been secretly looking for Yuki, along with Igneel, hoping to find them together one day, what he doesn't know is his Younger sister is finally on his trail.