True Nephilim take the form of giant humanoid beings, glowing from within with heavenly fire. They are incredibly bright to look at, and move as if they are drifting on light, rather than stomping as giants might. True Nephilim are still capable of speech, and appear to retain some semblance of their human memories and appearance, but largely ignore those around them, including people they once knew. However, they have been known to kill their own families and loved ones, as well as anyone who stands in their path.
The experience was described by Julian Blackthorn as feeling like he was on a mission, and being directed by a will greater than his.
After some time, a true Nephilim begins to falter and tire as the heavenly fire becomes too much for them to bear, and fissures start to appear on their bodies, from which fire starts to pour. At this point, the transformed Shadowhunter must either change back or be consumed by the flames.
|“||The land that we have gone through as spies is a land that devours its inhabitants; and all the people that we saw in it are of great size. There we saw the Nephilim; and to ourselves we seemed like grasshoppers, and so we seemed to them.||”|
–old eyewitness account of true Nephilim, Queen of Air and Darkness
In the early days of the Shadowhunter race, Shadowhunters had the ability to transform themselves into Nephilim at will, through a process long since lost to history. The need for true Nephilim arose from the fact that giant demons walked the earth during this time.
It was considered the ultimate sacrifice to turn into true Nephilim as the transformation into a giant being ablaze with heavenly fire usually proved fatal to the Shadowhunter involved. However, the Shadowhunters began to notice that many of those who survived were part of a parabatai pair, and that the odds of survival were far greater if one of the parabatai remained untransformed as an anchor to their partner.
The practice of becoming true Nephilim continued until approximately the 13th century, when giant demons disappeared from the world for some unknown reason, and the time of the true Nephilim came to an end.
It was after this that the few known cases of parabatai couples in love unintentionally transformed into true Nephilim occurred. The couples would go wild, killing the demon they were hunting, as well as their own families and any who tried to stop them, until they burned to death from the heavenly fire. At least two incidents are known to have been documented during this time: a married couple and two lovers, both parabatai pairs.
Rather than make these mishaps public, the Clave went to great lengths to cover it up as it did not want to lose the power of parabatai bonds, and it was thought that true Nephilim would not be needed again since the great demons had vanished. The matter was closed, until two more parabatai were reported as having destroyed a town before they burned to death, most likely from the heavenly fire of true Nephilim. All records of the incident among the Nephilim were destroyed; though a record of the story was kept in the Spiral Labyrinth, the belief was that the pair used powerful, warlock-like magic and were burned to death by the townspeople.
The Law against parabatai falling in love was passed not long afterwards and no explanation was offered aside from an ominous warning about a parabatai curse that befalls those who defy the rule.
The correlation between true Nephilim and the parabatai curse was not rediscovered until over 800 years later, in September 2012, when a large gathering of Shadowhunters and Downworlders witnessed the transformations of Emma Carstairs and Julian Blackthorn—a pair of parabatai in love and in the last stages of the supposed parabatai curse—into true Nephilim in Idris, during which they proceeded to kill various enemies, and almost destroyed Alicante and everyone in it. Their transformation once again revealed the existence of true Nephilim to the Shadow World, and created an opportunity for an appeal for amendments to the Law against parabatai falling in love.
Shadowhunters known to have transformed into True Nephilim:
- Unnamed married parabatai † (killed by heavenly fire)
- Unnamed parabatai lovers † (killed by heavenly fire)
- Emma Carstairs and Julian Blackthorn (survived; bond split by heavenly fire)