Dragon Slayer Magic

Dragon Slayer Magic (滅竜魔法 Metsuryū Mahō) is a form of Lost Magic used by Dragon Slayers.

Description
Dragon Slayer Magic is a branch of Lost Magic which allows its users to transform the physiology of their body into those of a dragon. As a result of this, those with Dragon Slayer abilities are able to change their body to their own element in both offensive and defensive styles. They can consume external sources of their natural element to replenish their own energy. They are also naturally immune to the effects of their own element that came from both their own person and to those from other sources, but must consume it through their mouths if they are to actually absorb it into their bodies.

Dragon Force is the final stage of Dragon Slayer Magic, though the exact conditions to invoke it are unknown. When Dragon Force is achieved, the Dragon Slayer's skin becomes scaly, similar to a dragon, and strength, speed, and magical abilities are enhanced, improving their combat capability significantly. Natsu Dragneel has achieved this at least twice; once after eating Etherion-infused Lacrima and again after consuming Jellal's Golden Flame of Rebuke.

There are two ways to learn Dragon Slayer Magic. The First Generation Dragon Slayers learn from Dragons and the Second Generation Dragon Slayers implant Lacrima crystals into themselves. There are also hybrids of the Old-Style and New-Generation Dragon known as Third Generation Dragon Slayers, who learned from Dragons and had Lacrima implanted into them.

History
This form of Magic was born over four hundred years ago during the Dragons Civil War. The Dragons that supported coexistence between humans and dragons came up with a strategy wherein they taught humans Magic and were asked to join the war. However there was a miscalculation, since some of the humans who learned their Magic started to kill all of the dragons.

First Generation
Dragon Slayer Magic used by those who have been raised by a Dragon and been taught their abilities.

Second Generation
Dragon Slayers Magic used by those who have Dragon Lacrima implanted into their bodies.

Third Generation
Dragon Slayer Magic used by those who are both raised by Dragons and have Dragon Lacrima implanted into their bodies.

Fourth Generation
It is rumored (however not confirmed) that when a first generation dragon slayer consumes the element of a dragon slayer powered by a lacrima (second or third generation) they gain that element along with their original and become a fourth generation dragon slayer. The only known case of this is Natsu's consumption of Laxus's lightning, resulting in Lightning Flame Dragon Mode.