The Keys of Fire by LoneStorm Fairy Tail

Runaway Lucy Heartfilia finally gets to join Fairy Tail, house and school for homeless kids. What she didn't expect was to be brought there by a pink-haired, pyrotechnic black belt with a blue cat, that she might start falling for him, or that this boy could help her solve the mystery behind the golden keys left by her mother that hold a deadly secret. High school ninja AU. Nalu.Rated: T - English - Adventure/Romance - Chapters: 51 - Words: 343,076 - Reviews: 4097 - Favs: 4,041 - Follows: 2,348 - Updated: Dec 23, 2015 - Published: Jul 25, 2014 - [Lucy H., Natsu D.] Levy M., Robert - Complete