Skill Book
Skill books are in-game items.
To be able to learn new combat skills and level up already learned characters' combat skills, players must use skill books. Skill books can be bought from Cattleya Organization NPCs, which are located across the game world. The books can be bought with the in-game Currency.
For a player to either learn or level up a skill for their character they must posses a skill book of corresponding level.
Hovering over a skill book promps a pup-up which describes information about corresponding skill:
A player can buy any skill books, but can use only those that meet the class requirement. For example : if the player has Knight as a current character class, the player can buy other classes' books, but can't use them. To be able to use other classes' skill books, the player have to change the class corresponding to the skill book of choice.