[@Sadu] See, this is why Cinderella World in Birth By Sleep is the best balanced world. We get to see the dark, broody bastard have a character ark where he learns that when you wish upon a star, dreams really do come true. Aqua actually helps in the story by buying time for Cinderella's escape and the character who's whole thing is that he feels small and insignificant in the world actually face a world where he is small and insignificant. It actually plays with characters themes while keeping the original story alive. Each of the characters has a role to play and a lesson to learn, as well as having tangible impact on the original story. It's the benchmark from which all worlds should be based.

The most fun world is probably Toy Story in KHIII, but that's entirely down to gameplay.

That being said, when i was running my D&D game, i introduced a system based on D-Links. Where, essentially, if a player interacted with a character enough, then they formed a Destiny Link with them. This gave them a unique Key-Weapon based on their new friend, with a unique ability. Kinda like the weapon transformations in KHIII.

Examples:
*Darkwing Duck gave a Pistol that also allowed them to Misty Step twice a day with a flashy puff of smoke.
*Elsa gave a Dagger that dealt Cold damage, as well as protected them from the effects of Extreme Hot and Cold Weather while holding it.
*Beshte gave a hammer that doubled their ability to hold their breath and gave them advantage to resist Fear.
*Peter Pan gave them a Dagger that allowed them to cast Disguise Self once a day.

This incentivised the players to actually get involved in the story, rather than just sit back and go with the flow.