The chaos is the dark force that the player has to fight in the end.Sally's dad, Franz, went to fight the chaos but never came back. (the Chaos caught him)
the chaos are rising again! the player is the true keeper of the monsters, and he/she must fight off the chaos.
On the last battle in story mode, the player will face the chaos master. The player would have to attack 3 dragsters, two of them are level 3 while one is level 2. after the battle, the player continues to chase after the chaos, starting to face more difficult monsters like Boarster, Hungerster, Jackoloster etc.