The toughest treasures in Octopath Traveler 0 are the Blue Chests and they require a special key for unlocking them. Restoring Wishvale and upgrading Aelfric Church to Level 3 will provide access to the Blue Chests. Follow this guide for directions on obtaining the key, unlocking the chests, and increasing your Helper Capacity.
How to Unlock Blue Chests
One of the unusual types of treasures in Octopath Traveler 0 is the Blue Chest. Unlike normal treasures, they require a special item to unlock. They contain more valuable loot than normal chests. There are four different types of chests throughout the game, and you will find Blue Chests to be the most difficult to find and unlock compared with the other three.
In order to gain access, first, you must construct a Church in Wishvale by completing Chapter 5 of the Kindlers of the Flame storyline. After Chapter 5, you will see Laurana again, and you will need to recruit her as a Cleric before going back to Wishvale.
Once there, focus on rebuilding the Aelfric Church. Upgrading it to Level 3 is essential, and doing so requires 12 Radiant Cornerstones. These items are earned by defeating Elite enemies scattered throughout Osterra, and by this stage of the game, you may already have enough to complete the task.
After the church reaches Level 3, the Blue Chests become accessible anywhere in the game world. As a bonus, the upgrade also raises your Helper Capacity to the maximum of nine, giving you more support during exploration and battles.
