The Library Key is a quest item used to unlock the hidden library door beneath the Second Sea. Its only purpose is to grant access to the room where players can obtain the Death Step fighting style, making it a required item for anyone progressing toward that fighting style. Once acquired, the key can be used to open the library door and continue the quest.

Obtainment:

The Library Key has a 10% chance to drop from the Awakened Ice Admiral, who can be found in the main hall of the Ice Castle. Defeating this boss also gives a small chance to obtain the Hidden Key, although its drop rate is significantly lower than the Library Key.
Usage:
The Library Key is required to obtain Death Step. After acquiring it, travel to the Ice Castle and use the key to unlock the room on the right side of the castle's corridor, where Phoeyu, the Reformed is located. Access to this room is necessary to continue the Death Step unlock process.
Additional Information:
• The Library Key, along with the Hidden Key, Water Key, and Red Key, is lost if the player dies or leaves the game before using it.

• Unlike the Hidden Key, which can drop from any enemy in the Ice Castle, the Library Key can only be obtained by defeating the Awakened Ice Admiral.

• The Library Key can be used to permanently unlock Phoeyu's room even if the player does not yet meet the requirements for Death Step. Once opened, the door remains unlocked for that player across all servers.