Keys

Keys are unique items used to open specific locks. Some of these locks can otherwise be opened like normal ones, while some can only be unlocked with the right keys. Keys are found inside certain containers and enemies' dead bodies, or by accepting certain quests.

Book I
In Book I, keys take up space in the inventory like other classes of items, and are automatically and permanently removed after being used.

Book II
In Book II, obtained keys will be moved to the Key Ring instead of the inventory, and can be viewed and used at any times.