Balmung & Lord Kaho's Horn

The Royal Messenger in Prontera runs a royal quest that trades rare materials for one of two top-tier rewards — the Balmung blade or the Lord Kaho's Horn headgear. This is an expensive high-end quest: on top of a pile of elemental components, each branch costs 1,000,000 zeny. You pick the reward up front, since the two branches need different materials. Gather everything beforehand — the NPC only hands over the item if you have it all in your inventory at once.