It can just be "let's visit this world." In that sense, something simple like Dagobah (visiting Yoda for some training)
How awesome would it be if Yen Sid sends Sora to train at his ''old friend'' in another world and we got to see the Dagobah scene pretty much 1-1 except with Sora instead of Luke. Have Gummi ship malfunction and Yoda starts ripping it apart with Donald getting pissed off :lol.
Would it be too much for Sora to learn ''Light push'' ability?
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As for how I would make a whole traditional KH style world out of Star Wars? Well I think there is really only one logical place to set it in if we don't want to do multi location style (tho even that is possible but I don't think it is neccessary at all. The place would have to be Death Star from Episode 4. First movie for the first appearance in the series, the most iconic location possible and it is a place where all the important characters from the movie are together at one location: Solo, Luke, Leia, Obi-Wan, Vader, Chewie and the droids are all there along with stormtroopers. Also I have talked about this scenario before but here I go again:
The world would function kinda like Monstro where the party is more forced to land than actually it being their original destination. At the middle point of your gummi route you
start hearing this as TIE fighters attack the gummi ship and the gummi route changes to a traditional Star Wars type black space with stars. You get some dogfighting with the TIE fighters instead of heartless ships (bam, that's another iconic SW thing in right there, space battles).
At the end of the route the Death Star tractor beam grabs the ship just like in the movie and the party is thrown into prison by Vader and troopers to wait for questioning. While they rot in the cell they get busted out by Luke/Han/OW while searching for Leia. Here they will give a brief exposition about where they are and about the empire being the bad guys and who Vader, the guy who captured Sora+friends is and that they weren't trying to free them but Leia instead so they just bump into each other by accident.
Here it is important however to have the CHARACTERS, not the plot take importance. The whole plot of the original movie IS NOT IMPORTANT. It really is not, all that is important is the situation that the characters are in and how they react to it naturally without trying to tell the whole story of the movie, the idea here indeed is that the Death Star is the only location that appears (plus the space part) and anything that has happened in the movie outside that is thrown into the garbage unless it is absolutely needed to as a reference.
Now this next thing is just a silly idea by me but one fun way to tie the world into the overarchin KH plot (as this is a forced world, not something Sora was planning to do) is for Obi-Wan to actually be one of the rare characters to recognize the Keyblade and it's importance (kinda like Triton in KH1) as the whole Jedi-Keyblade thing are basically kinda the same thing. You could have him tell that he actually met Xehanort (or Eraqus, Yen Sid, whatever) as a young man or something while YX was travelling the worlds and have them share some small conversation about it and perhaps reveal a little bit about Xehanort when he was a young man. Make him kinda have Xehanort take Vaders place in the way he talked about him in the movies. Maybe Xehanort was indeed a great warrior and a good friend back in the day or something. Also this would make the point that X was a respected Keyblade Master back in the day. Anyway this is just a silly idea that you could put in there, not important at all.
Before throwing Leia into the mix you should have the main trio, OW+Han+Luke show their personality and have time to do some scenes before rushing with the plot. Characters and the way they react to you is the most important part about the cameos. Then after you have accomplished that you have them rescue Leia like in the movie. Boss fight against the garbage dump monster (or have it be a heartless in there but similar in that it's hiding). Now, Obi-Wan loses to Vader in a duel but one of the big questions I have is: should Vader be a boss? It kinda could feel a little forced but then again you kinda... need to have a Vader boss if ya know what I mean. Anyway Vader blocks the parties way, they defeat him and escape. Have some cool space battle part 2 where you are working alongside Millenium Falcon. The end. Returning to Death Star later on to gather treasure chests and whatnot has to just be passed as neccessary Vidya Gaem sillyness.
Credits scene is Luke blowing up Death Star. That is one way the world could be done and I do feel that Death Star (and new hope) is the perfect place to introduce the franchise to KH. You can basically go to many places after that if SW returns to the series, both sequel and prequel.
edit: One more thing: I before was very optimistic about SW making an appearance in KH3 but after the whole ''canon purge'' I do think things have changed. Not really because of KH appearance being canon, obviously it would be non canon by default but it is clear they have put a tight leash about how they will handle SW before ep7 comes out.
Then again seeing stuff like Rebels means it can't be THAT tight of a leash
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