A minor celestial spirit that serves as a pet to Lucy Heartphilia of Fairy Tail and as a guide to Haru of Rave Master, along with assisting them both in their journey's.
Plue originally appeared in the Rave Master series, another creation of Hiro Mashima, as the companion to the series protagonist Haru Glory on his quest for the Rave Stones. Plue played a major role to the series plot. Plue is first seen in Episode 1 and Volume 1 of Rave Master. He first assisted Shiba, the previous Rave Master to Haru. Haru finds him while fishing in his home town at Garage Island, however we actually first see Plue in the anime when there is a flashback of him and Shiba trying to finish off the Dark Bring.
Plue is a minor Celestial Spirit that serves as a pet to Lucy Heartphilia in Fairy Tail, and has less of a reoccurring role has he once had in Rave Master. Plue serves as a pet for Lucy when she walks along the river. Also, Lucy uses Plue to distract her enemies: Sherry during Galuna arc and Daphne's Lizard men during Dragon Filler arc. He appears in Fairy Tail episode 3, volume 1, and Fairy Tail OAD 1.
For Rave Master, Plue, who is created Hiro Mashima, is originally a doodle (unknown volume). It is interesting to note though, that it can be assumed Plue has been a Rave Master Guardian for all his creation time, even though it was never stated. Another note for the pronunciation of Plue's name, (in Hiro Mashima's notes - unknown volume) Plue is pronounced like the color, "Blue."
Like Siegrain/ Jellal, Plue is a fan service to Rave Master fans when Hiro Mashima put Plue in Fairy Tail.
Plue is more human in Rave Master than Fairy Tail. In various scenes like the passing of Gearhound and Clea, Plue cries for his friends, and after he cries, he has the will to move on. Plue will get hungry, try to communicate to people, offer bugs to Shiba, or help his friends. This makes Plue have human qualities.
In both franchises, Plue does not really change in personality or appearances.
In Rave Master, Plue holds the Rave Stones and possesses a more active role. His nose can be used as a weapon that can stab through most things very easily. He also possesses some healing powers that enable him to slow down blood loss of potentially fatal wounds. Plue also seems to be able to sense Rave Stones which are close by, as well as using various modes in battle that increase the power of the Rave Master.
In both series he is only able to say his own name, and he is characteristically always shivering. He does this when he senses danger or Holy Bring, he also did this while he was nervous or had some type of anxiety.
In Fairy Tail, he functions largely as a reference to Rave Master and as a cute pet for Lucy, who is enamored with him. He is unable to talk and mostly communicates with motions or dancing. He is most often considered a dog, being represented by The Canis Minor constellation. He seems to lack any combat abilities, and often functions as a mascot character alongside Happy.
Note: This only for Rave Master since Plue is only a pet in Fairy Tail. This section is created because (according to Haru Glory) Plue is a Rave warrior who eats, sleeps, cries, and fights like a human being.
Unlike Fairy Tail, Plue can attack with his sharp, carrot-like nose. His nose can shatter Dark Bring, and Elie can use him like a projectile. He is also used during battles with the Rave Master, empowering the Rave Master by using various combat forms. This type of power is first shown in Rave Master: Episode # 1, while Shiba was fighting the Dark Bring, Plue assisted him by giving him power and giving power to the Ten Commandments Sword. This was the time before the Rave was broken into several pieces and scattered throughout the world, we know this because Plue would wear them around his neck, calling upon their power only as a last resort.
For Rave Master: Plue is famous for being mistaken for many animals or things. At first, Haru thinks Plue is a fish while Elie thinks Plue is an insect. Also, Haru calls Plue Shabutaro until Shiba corrects Haru. Go, an exhibitionist movie actor, calls Plue an alien (sub). Hamrio Musica calls Plue a cat or a chihuahua The few people who get Plue's animal right is Cattleya, Shiba, and Ebi. It is also mistaken that Plue has a carrot type nose, when it appears and acts more like a drill.
For Fairy Tail: Lucy Heartphilia is the first one to acknowledge that Plue is a dog due to his constellation.
Rave Master: An assassin named Dr. Schneider calls Plue, an imp, in the sub version compared to the dub version, he calls Plue, a river rat.