Heavenly fire is the divine fire of Heaven and the power that runs through the veins of angels.
The heavenly metal adamas is one substance infused with generic heavenly fire, and it is this fire that powers seraph blades. The power of the heavenly fire in seraph blades becomes even greater when the spirit of the angel's name is called, imbuing the blade with the power of the angel and causing the blades to glow from within. Steles, also made of adamas, also contain heavenly fire; as such, runes drawn with steles, though harmless on Shadowhunters' skin, save for a slight stinging sensation, cannot be withstood by normal paper or the skin of any other being.
Weapons of Heaven, one of them being the sword known as Glorious, also carry heavenly fire within them. Using the weapon on a person will imbue them with heavenly fire as well, which ultimately burns any form of evil found in him/her; if the person is more evil than good, then it will also burn the life from him/her.
In some rare cases, heavenly fire may engulf or inhabit bodies of mortals. Though heavenly fire would normally kill human beings, few people are known to have briefly possessed heavenly fire and survived, including:
- Tessa Gray, whose veins blazed with heavenly fire as a result of Changing into the form of the angel Ithuriel, who was trapped in her clockwork angel necklace. She survived the effects of the heavenly fire thanks to Ithuriel's protection, and this also affected her warlock abilities.
- Jace Herondale, whose body was filled with the fire after being stabbed by Glorious to sever the twinning bond between him and Sebastian Morgenstern. Because he was more good than evil, he survived the attack, though he was burdened with the fire burning into his veins until Clary Fray was able to utilize a rune that transferred the fire to another host; this time, the sword Heosphoros. The heavenly fire-imbued sword was then used by Clary to stab Sebastian, and the fire burned away both the evil within him and his life, before finally being burned up itself.
- Jem Carstairs, also known as Brother Zachariah, whose body burned with heavenly fire upon contact with Jace after he had been overcome by an attack from the fire within him. The heavenly fire had a different effect on him, however, as he only had brief contact with it. Though the heavenly fire also burned through him as it did Jace, the fire merely burned away the evil within him; specifically the presence of the demon drug yin fen, and cleansed it from his body. This, along with over a century of being in his dormant state as a Silent Brother, helped cure him from his addiction and dependence on the drug. Additionally, since the yin fen was also presumably only his illness that bound him to his partial Silent Brother state, he was also freed from the runes and spells that kept him in the Brotherhood and was safely reverted to his mortal self.
- Julian Blackthorn and Emma Carstairs, both of whom's body burned with heavenly fire when they were transformed into True Nephilim as a result of the parabatai curse. The fire inside them caused them to act for the angel's will and gave them no control over themselves. In this state they destroyed the Riders of Mannan and killed a few other Shadowhunters as well. They may have killed more had their family and friends not talked them down. When they returned to their normal state, the heavenly fire had burned away their parabatai bond, leaving them with no trace of it ever having been there.