Premise: As the Guardians of Light and Seekers of Darkness are clashing, Sora notices an unknown person that looks like a Darkling. As Sora chases unto it, the Darkling opens a portal and goes into it, but leaves it open. As Sora approaches it and contemplates it for a bit, a ray of light comes out from it, into the sky, and opens an even bigger portal that sucks everyone into it. When they open their eyes, the Guardians are greeted by Cosmos, Goddess of Harmony. She tells them that the evil God of Discord, Chaos, has summoned opposing warriors from their realm (Sora's) in order to wage war on the balance of the universe and recreate it in Chaos' image. Cosmos shares a piece of speculation concerning Chaos' sudden outburst, perhaps being related to the sudden appearance of an outside entity. Her description coincides with the entity Sora saw. Since he doesn't want to change the focus from everyone, Sora tells Riku and Kairi to secretly look over about the Darkling.
Gameplay: Similar to the first two Dissidia games.