• Now that you have gathered the necessary pieces, Gerolt reveals the identity of his secret materia: your relic weapon nexus. Indeed, he reasons, if all the combined energies bound to the weapon could be made into materia, the very souls you have worked so hard to cultivate can ascend to the new host. But whether such an outrageous thing is even possible remains to be seen. To find out, Gerolt bids you seek the counsel of Master Mutamix at the Bonfire.
• Mutamix readily agrees to lend his aid to your cause. Inform Gerolt that the materia master is ready and willing.
• Delighted that Master Mutamix has promised to help, Gerolt now says everything is in place. Speak with Jalzahn when you are ready to recreate your Zodiac Weapon.

To upgrade your weapon, speak to Jalzahn after completing this quest and trade him the 4 items.

• The name of this quest most likely refers either to His Dark Materials, a trilogy of novels by Phillip Pullman, or a passage from John Milton's Paradise Lost, the namesake of the former.