Chaos difficulty is a secret unlockable difficulty in Tales of Arise. It’s the highest difficulty in the game and needs to be unlocked first. By default you only have 4 difficulties (Story, Easy, Moderate, Hard), but this will add a 5th difficulty that’s even more challenging.
How to Unlock Chaos Difficulty: Beat Dohalim Solo Ultimate Challenge (Level 60) at the Training Grounds (in Menancia > Viscint) to unlock artifact “Devil Sculpture”. This artifact enables chaos difficulty. Due to the high level requirement you won’t be able to unlock this until the end of the game or after the story.
That’s all there is to unlocking the secret Chaos difficulty in Tales of Arise.
For more guides, check out the complete Tales of Arise Wiki & Strategy Guide.