Demon Boss Souls are special Souls dropped by the final bosses of each area in Demon's Souls. These Souls can be exchanged for powerful weapons, magic,

To open up the possibility of using Demon Boss Souls to make new weapons, you must first use the Flamelurker’s Searing Demon’s Soul by giving it to Blacksmith Ed to unlock Advanced Weapon Crafting. Many of these new crafting recipes will require other powerful weapons in addition to the boss soul to create something new – but they can also be given to spellcasting NPCs to learn new spells.