For those who have not completed Xenoblade Chronicles, this page or section may contain spoilers regarding the plot. Discretion is advised.
The AP cost of levelling up an art depends on both the art and the level. The cost for each additional level follows a consistent pattern:
For example, raising Shulk's Back Slash to level 2 costs 200 AP, while raising his Slit Edge to level 2 costs 220 AP. Raising these arts to level 3 costs 400 AP and 440 AP respectively (2x200 and 2x220), while raising them from level 5 to level 6 costs 2,400 AP and 2,640 AP respectively (12x200 and 12x220).
All physical and Ether attacking arts at level 1 have an additional hit rate of 5%. Each level increased will increase the hit rate further by 5%, up to a maximum of 25% at level 5 or higher.
Furthermore, arts will have their effects enhanced by levelling up. These enhancements may include, but are not limited to: increased aggro added to enemies, increased damage, increased healing power, increased buff or debuff duration, and reduced cooldown time.
Initially, arts cannot be raised beyond level 4. Intermediate books allow the art to be raised as high as level 7, and can be bought from shops. Advanced books allow the art to be raised to level 10, even if an intermediate book for that art has not yet been learned or obtained, and can be found in gold chests dropped by monsters above level 45, or in special chests found in certain locations. These sources are mutually exclusive; there are no Advanced books available for sale, nor are there any monsters that drop Intermediate books.
After an art book is obtained, it is necessary to select it in the inventory and read it to unlock the additional levels of that art. Art books can only be read once, and cannot be used if the character has not yet learned the Art itself or is not in the party. Intermediate books cannot be used if an Advanced book has already been learned. Excess Art Books can be sold to shops.
(Note: There are two separate Art Books for the two characters who learn Guard Shift. These books are not interchangeable.)
Art Book Sources
Generally, the drop rates for advanced books are extremely low—some have a drop rate of less than 1%. Higher level monsters tend to have higher drop rates. The save and reload method can be used to open the same gold chest repeatedly until a desired advanced book is obtained. Up to two of four named books can be acquired without duplicates (e.g. a given monster can drop up to two of either Back Slash, Battle Soul, Slit Edge or Light Heal).
|[[Slit Edge (XC1)|]]||Ether Light (Colony 9)|
|[[Back Slash (XC1)|]]||Ether Light (Colony 9)|
|Light Heal||Ether Light (Colony 9)|
(After the Mechon raid only)
|Shaker Edge||Weapon Shop (Frontier Village)|
|Air Slash||Refugee Camp (Bionis' Leg)||
|Shadow Eye||Refugee Camp (Bionis' Leg)|
|Battle Soul||Weapon Shop (Frontier Village)|
|[[Stream Edge (XC1)|]]||Refugee Camp (Bionis' Leg)|