The strange creature that Haru discovered, Plue is the Rave Bearer, and is able to sense the presence of the other Rave Stones. Plue's nose also has the ability to destroy dark brings. Plue is quite fond of sweets - especially lollipops. Plue hates pudding. He has the ability to utilize the rave of conflict which powers him and Haru up.
Plue has since shown up in Fairy Tail as one of Lucy's stellar spirits (Nicola, Canis Minor) and quickly named Plue and has been noted to only agree to be summoned on Tuesdays, Wednesdays and Thursdays.
(Source: Wikipedia)