You may come across treasure chests while investigating layers or after winning battles. However, they are guarded by traps, and if you fail to unlock them, you can't get the treasures inside. Astrals have unlocking skills, so use them to your advantage to acquire more items.
When the Danger Level of the treasure chest reaches the MAX, the trap is sprung. Traps can cause damage, inflict ailments, warp you, or have other effects. Astrals may become impure and will be unable to fight. When attempting to unlock treasure chests, pay close attention to the danger level.