Bruni is one of four elemental spirits in the Enchanted Forest, the others being the water spirit the Nokk, the Earth Giants, and the wind spirit Gale. To the Northuldra, he is known as simply the Fire Spirit. When set loose, he sets the entire forest ablaze, creating beautiful but violent fires all throughout his path. But when in a passive state, he can create small flickers of flame to help the Northuldra tribe.
Thirty-four years before the events of the film, the then-monarch of Arendelle, King Runeard, murdered the leader of the Northuldra in a false gesture of peace. Bruni, along with the other spirits, was so consumed with rage by the treacherous act that they turned against all the humans. A curse was placed over the Enchanted Forest and trapped everyone involved in the fight within the mist, and the elementals entered dormancy. The only way to undo the curse was to destroy Runeard's dam—the object that sparked the conflict—that would sate the elementals.
Role in the film
Bruni appears as a flame that descends upon a face-off between the Northuldra, Arendelle soldiers, and the party consisting of Elsa, Anna, and their friends. Using her ice magic, Elsa puts out the flames Bruni generates and chases him into a small hole. A cornered Bruni simmers down and tries to hiss at Elsa; Elsa gestures to the salamander that she means no harm, extending her hand to as a sign of goodwill. Though cautious, Bruni reluctantly crawls up Elsa's hand, accidentally burning Elsa's hand due to his heat, but she manages to calm him down, and when he calms down, so do the forest fires. Elsa then offers Bruni some snowflakes that he happily gulps down, establishing a newfound bond with Elsa. Once calm, Elsa lets him off on his way, as Bruni tilts his head to the next step of Elsa's journey: the north, where the same mysterious voice that Elsa hears is coming from.
He continues to observe Elsa's party from the treetops along with Gale. Bruni is later seen watching Olaf's remains floating away, looking upon them despondently. After Anna destroys Runeard's dam, the spirits make peace with the humans and welcome Elsa as the fifth elemental spirit and guardian of the forest. Bruni is last seen following Elsa, and Elsa provides him a pile of snowflakes that he lands into and happily feasts upon.
- The nickname "Bruni" was given to him by Anna, Elsa and the others of their group according to supplementary material, though the name is never used in the film itself.
- In European mythology, specifically in the works of Paracelsus, the element of fire was represented by a mythological creature called a "salamander", which roughly resembled its namesake, but often varied in depiction (sometimes depicted as a dragon or lizard rather than an amphibian). Some scholars believe that the myth began as the result of people burning logs that salamanders were sleeping in and believing that their escape attempts were the salamanders being brought into existence by the flames. In some works, the creature was attributed as a symbol of poison in addition to or instead of fire.
- Out of the four spirits, Bruni is the only one that is technically a living creature.