After Xehanort's defeat, the worlds were saved by Sora again, but that was just temporary. There are still threats out there, so the Keyblade wielders who fought against Xehanort form an organization called "Light Guardians" to protect and help those who need it.

After finishing the last mission Yen Sid gave him, Sora receives a new one and ends up in Fiore. There, he meets some people who need him to defeat the Heartless that are invading their world and now he must save this world with the help of a powerful guild.

Yen Sid sends Sora to Death City because it's being invaded by Heartless. Sora goes there to eradicate them and keep the city and its residents safe, but soon he finds out that the Heartless aren't his biggest problem.

Some time during the plot line of "Kingdom Hearts II," Sora, Donald and Goofy stumble upon a new world, where people turn into weapons, that is ruled by a strange man wearing a skull mask, and Sora can't summon the Keyblade. R&R