Rave Master

Rave Master (called Groove Adventure Rave or simply Rave in Japan) is a previous manga of the author of Fairy Tail, Hiro Mashima. Which tells the story of Haru Glory, a teenager who becomes the second Rave Master and is destined to bring peace to his world and save it from the threat of Dark Bring (Shadow Stones in the English verison). Along the way he gains friends who join him on his quest and slowly unravels the mystery of the Rave Stones (his power source), The Dark Bring, his destiny, how it affects those around him and the fate of the world in general.

Many elements of this series pop up in Fairy Tail often. Most notably Plue, Haru's guide, being one of Lucy's Stellar Spirits. One can also spot characters from Rave Master in the background. A chapter cover even featured Lucy and Natsu dressed as Haru and Elle from the series as well.

For more information of the series, check the Wikipedia article on Rave Master or its Wikia site.