Dragons

Dragons are big scary lizards that breathe fire... Right? Well, no. The category of "Dragon" refers to the creatures from which the Dragon's Heart originates, and true Dragons are in fact one of the Great Races of Nexus. That is, there are a great many creatures which are not the classic "Dragon" archetype, and many creatures who seem to be "Dragons" but are not.

Famously, many continents are home to large energy-breathing monstrosities, such as the Naco Agul, Anjanath, and (most frustratingly) Rathian and Rathalos. These are large creatures, some resembling dragons greatly, which breathe fire, ice, lightning, or other elements. And despite the Rathian and Rathalos literally being large, scaly winged creatures that spit fire... None are dragons. What's the deal?

Well, the Dragon's Heart is more than a nice-sounding phrase. It is a wellspring of special magic that can be refined and cultivated in ways that most others cannot be. It is sometimes used to fuel magical breath weapons, but also spellcasting and other magic talents. I'd like to see the Rathian use it's little fire sac to cast Lightning Bolt. The Dragon's Heart comes from the Dragons' connection to the Dragon Eyrie, and their direct line to the rulers of this Plane(Which also happen to be their creators); The Draconic Pantheon.