The Fire Spirits Yumir summoned told him of an ancient spirit named Flarestorm, which was bound to an incinerator and corrupted by the Balaur. Flarestorm--who is actually a conglomeration of smaller flames--must be vanquished repeatedly to return each individual Fire Spirit to the flow of Aether. You went to the Blue Flame Incinerator in the Beshmundir Temple and vanquished Flarestorm, releasing one of the spirits.