The Eden Soul is an item dropped by mobs native to Eden. Eden Souls are used in the crafting of Eden Blocks, which are used to create the portal to The Wildwood.
All mobs in Eden (besides the Angry Bunny, though normal Bunnies still drop souls) drop between 0-2 Eden Souls (this figure varies from mob to mob). If the player uses a sword with a Looting enchantment, this figure can be increased.