As an added bonus, all Ashen loot handed in during the Event will earn you increased rewards and help raise your Emissary Grade, to make finding those Bottles even more enticing...
Meanwhile, the forecast for volcanic activity in the Roar suggests things will be surprisingly quiet during these Ashen Expeditions, allowing you to hunt down Ashen Message in a Bottle Voyages and their spoils in relative peace - and pursue the rumours of a unique unlockable reward for doing so. Good luck!
