well if a Miyazaki Movie became a world for KH2 here are my suggestions and summaries.
Spirited Away: Sora and the gang accidently step into the spirit world and end up trapped. while wondering aimlessly, they run into Haku (or he ran into them) and he knew who sora was at the start. Haku tells our heros that Yubaba (the witch who runs the bathhouse) has taken control of the heartless and started using them for her own gain. from here you have to sneek into the bath house undetected. after entering the bathhouse via the furnace room, you have get to the top floor without getting cuaght (and this could be a problem since spirits can smell humans off the bat.) once you reach the top, you see Chihiro trying the convince Yubaba to give her a job. Yubaba then notices sora and his pals. she then tries to get you to leave using her magic. a small battle with Yubaba ensures but is cut short when the baby is woken up. sora takes advantage of this by threating to make more noise unless Yubaba give them jobs at the bathhouse. Yubaba agrees dispite the fact that she "lost" to a human. sora and the others sign their contracts then Yubaba collects them and magically removes the names all except sora's for some reason doesn't come off. Donald is now named Zing and Goofy is now called Chu. Haku comes in a gives each character a different job. Goofy/Chu: security. Donald/Zing: cooking department. sora and Chihiro: cleaning duty. after this the gang is seperated. each character has a list of sidequest and minigame that they must complete. the rewards range from items to munny. while doing one of the Sora/Chihiro sidequest, they let a mysterious creature in ( he'll be a huge problem later on). after the first night, you mett Haku outside the bath house. Donald and Goofy all already strarting to forget their real names. Haku explains that Yubaba controls people by taking away their names and if full forget they can't return the human world. sora ask how he still remembers his name. Haku dosen't quite know that answer but tells them to return to the bath house before the are caught as they reach the sora looks back and sees a white dragon flying in the sky. later a stink spirit show up and the gang is assembled to make it happy. when it entered, it's foul aroma stinks up the entire area, even the heartless don't like it. minigame starts as you try to please the stink spirit. you soon learn that it really isn't a stink spirit but a river spirit trapped in alot of junk. a new minigame starts, which similar to tug a war as you try to pull the junk out. after the event you are rewarded a medicine ball. sora tries to eat but ends up spiting out. later that night the same creature that you let in starts gobbling down heartless. during this it shallows a talking frog allowing to speak and it can create gold from own hands. the next day sora wakes up and sees that Haku (in dragon form is being attacked by Sky-bladers ( a type of nobody that looks like a white denoxys and attacks in large numbers). after a few attacks Haku ramms into the building, bleeds all over then starts flying to the top of the building. while trying the find Donald/zing and Goofy/Chu. sora and Chihiro bump into the creature then start heading outside. an event challenge starts. you have to press the triangle button at the right time so you can reach the other side.
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this is all i'm writing for now but edit the rest later.