Ok, the second game has hidden scenes from //SIGN which can be seen at Delta Hidden Forbidden Holy Ground, there are 4 total, so go there at the end of the game 4 times to see them all, seeing these will get you the Memory items, which are needed to person the Phantom quest in the third game...
Sora is freed after you beat a side quest dungeon in the third game. You get the item "Sora's Blade" for beating it, which are replicas of the katars Sora uses.
"Hark he of Fair eyes, I am CRtwenty of the Azure Keyboard!"