Original: Refusing to accept defeat, Xemnas separates Sora and Riku from the others to face them in a final battle that ends with his demise. Though initially trapped in Xemnas' realm, Sora and Riku are able to return to their world after reading a letter from Kairi that reveals the door to light.
Simplified: Near the end of the game, Sora, Kairi and Riku reunite and destroy Xemnas.