From Final Fantasy Wiki

Inward Chaos is an optional story mode playable in Dissidia Final Fantasy. In the Japanese version, it is unlocked after defeating Chaos for the first time in Shade Impulse (access to Shade Impulse is only available after all ten Destiny Odysseys are completed). In the NA/EU/AU version, it is unlocked after beating Shade Impulse, all ten Destiny Odysseys, and both Distant Glories (for the Western releases, Shade Impulse is unlocked after beating only a single Destiny Odyssey).

Inward Chaos has five stages in which the player must fight all the heroes and villains of the Dissidia cast (with the exception of Cosmos who is neither a boss or a playable character), with the fifth holding Chaos in wait after all foes are defeated. The opponents begin with a level 92 Warrior of Light and get progressively harder until maxing out at a level 110 Chaos, fought chronologically through all the heroes, followed by the villains. It is the most difficult story mode in the game.

All opponents will have level 98-100 equipment and one summon each with the exception of Chaos who, although he only has level 1 equipment, has the unique summon Shinryu and again must be fought three times before defeat. In this mode, Chaos is easily the most difficult boss in the entire game.

Story

The player is spoken to by a mysterious voice which challenges the player to continue forward against the strongest opponents. Shinryu is revealed to be the being behind the voice, and he states the this world is an alternative dimension in which Chaos has never known defeat. Upon the warrior's defeat of Chaos in this world, Shinryu realizes that the warrior's power is far greater than that of any god, and that his next creation will be a world through the eyes of someone like the warrior, rather than of one who stands high and powerful.

Level Bonus

Stages

Inward Chaos-1

Inward Chaos-2

Inward Chaos-3

Inward Chaos-4

Inward Chaos-5