Here are my ideas for the first 3 seasons (KH1, CoM, Days and KH2):
- Kairi getting kidnapped only once
- Room for only one character to keep the name, "Ansem" and the other gets a new name
- Ansem: Seeker of Darkness keeps the name "Ansem"
- Ansem The Wise's name will change to Count Sharuman The Wise (not the best name to come up with, but it's just for a good reference and is better than just him being Ansem)
- Riku will receive his Way to the Dawn after defeating Ansem one last time
- Naminé won't return to Kairi
- Riku won't be blindfolded and will not turn into resembling Ansem, but rather his dark form
- Xion not being forgotten from existence
- Roxas wields Oblivion and Xion wields Oathkeeper
- The stronger bond between Roxas and Xion (one point they start to fall in love)
- Chain of Memories being only 6 Episodes (meaning getting rid of the Disney Worlds)
- Atlantica being in Season 1 only (and only in KH1)
- Same thing with Hundred Acre Wood
- Sora still remembering his battles in Castle Oblivion after waking up from the Egg pod
- Zexion and Lexaeus need much better portrayal
- Some scenes from the KH2/Days Manga to make brief appearances
- Xemnas getting a nickname title (Seeker of Nothingness) for just maybe one scene
- Better portrayal for the Final Fantasy Characters (especially for Cloud and Sephiroth)
- Mickey not being present seeing Terra-Xehanort in a flashback
- Riku vs. Xigbar in Land of Dragons
- Naminé assisting Riku to insure him about the darkness
- The scene between Xigbar vs. Xion: Xion takes the appearance of Strelitzia instead of Ventus
- Xion being a Kairi instead of just being a Sora Replica
- Xion's origins in the same way Roxas and Naminé were created
- More scenes of Riku and Maleficent in Season 1
- Roxas and Xion being tasked to do villains stuff like fighting the good guys instead of a bunch of Heartless - Xion taking the appearance of Kairi instead of Sora, while Roxas sees his reflection of him being Sora
- Roxas lost his memories of what he remembers in the KH2 Events
- After fighting Axel the second time, he remembers everything again, including Xion and grows so much grief after losing her There's a lot of changes I have in mind, but it'll take a long time to even justify