Essence of the Soulstream, known as Demon's Extract (悪魔のエキス / あくまのエキス) in Japan, is an item from Gargoyle's Quest and Gargoyle's Quest II. It is not required and it is possible to complete the games without finding it, but it can be of great assistance. It can be used from the menu to fully recover Firebrand's life, but it can be used only once per life or level. It automatically refills after a level, or if a life is lost.
This item also appears in Namco × Capcom as the consumable item #30.
In Gargoyle's Quest, going left from the fork shown in the picture leads to the Essence of the Soulstream. Strangely, if King Breager takes all of Firebrand's powers and items, this is one of the only things not taken away.
In Gargoyle's Quest II, the essence is obtained from a researcher in the laboratory from the King's Palace that is studying it, but first he needs Achelon's Water and Dagon's Scales to create it. Achelon's Water is in a vial hidden near Mt. Imaus, and Dagon's Scales is obtained by defeating Dagon.