The Immortal Flame are only one of the Six fingers of Ahura, other six are; The Violent Wind, The Freezing Sickle, The Earth Impale, The Light Bringer and The Moon Shade. All of the six are once held by Kali but the other five was destroyed...
Among the collection, The immortal Flame is the flame affinity weapon. Once neglected weapon that was not noticed its power. The second occurence of this weapon is at the Book of Dragons: Tainted Blood, where it was wielded by Susano-O. Then, it was wielded by Wilhelmina Crimsonwing whom passed this weapon to her son, Siv Valentine.
The Immortal Flame has two forms, The Anti-Army and The Anti-Deity. In Anti-Army Form, it remains a form of a Great Sword. It can passively access all of its powers. But in Anti-Deity form, it will change into a Scythe, but it requires to be activated and namely, only Siv Valentine was able to activate it.
Unnoticed by some characters in the story, Immortal Flame holds a great abilities. It grants the user to amplify its power, literally means multiplying itself upto the limit of ten million of him with equal power. And, same with the Iceied Flayre, it can imprison souls of the slain.
The Immortal Flame was not activated until Siv Valentine finally wield it. As one of the Ink of Life Dependent weapons, The Immortal Flame requires the user to be an Immortal. Siv Valentine, is an execption, as he was born as an Immortal, due to mixed blood of Dragon and Lotus Demihuman races.
Notably, Siv Valentine has a Jinn-Lotus Form, the Phoenix. Formerly, he have a blue flame but when he wield the Immortal Flame, his flame changes into black which known as the most deadliest flame, one touch of it will wither the victims life.
Because of it's popularity during the war against the God of all Gods. Siv Valentine was reffered as The Immortal Flame.
In the Great Harvest, it was revealed that a certain cult was formed naming itself as The Order of Immortal Flame. But Siv Valentine never acknowledge the cult and just leave it, because Mortals has no relations to Deities' power after Ragnarok Exalt Era.