Square Enix originally showed concept art of a Kingdom Hearts III level based on Big Hero 6 at the 2015 D23 Expo. Finally, three years later, Square's showing off footage of the world in a new trailer focusing on Sora's adventures through the city of San Fransokyo. Additionally, several other features and hints toward the plot as a whole were touched upon.
In the Big Hero 6 level, Sora meets up with the heroes of the titular Disney film. Big Hero 6 is a 2014 Disney animated movie and centers around, aptly, six fledgling superheroes who band together to combat a mysterious, nanobot-controlling villain named Yokai. It's also the first animated Disney film to be based on a Marvel Comics property, albeit loosely.
Baymax, the pudgy robot who can suit up in an Iron Man-esque suit, is so far the only character to be shown off as a true party member, but Sora, Donald, and Goofy will also be enlisting the help of Hiro, Go Go, Honey Lemon, Wasabi, and Fred. It's yet to be revealed if their original English voice actors from the film will be returning to voice the characters again. The Big Hero 6 world is a sprawling cityscape based on a fusion of Tokyo, Japan and San Francisco, California. While the city is named San Fransokyo in the movie, it's unknown if this will be the name of the level based on it.
In addition to showing off the new level, the trailer gives more hints toward the storyline as a whole and shows off the new-and-improved Gummi Ships. The Gummi Ships were a quote-beloved-unquote feature in Kingdom Hearts and Kingdom Hearts II used to traverse between worlds, and it looks like Kingdom Hearts III is significantly upping the customizability of the ships and at least part of the missions involving it.
Kingdom Hearts III will release in Japan on January 25th, 2019, followed by a worldwide release on the 29th. It will be available for both the PlayStation 4 and Xbox One, making it the first Kingdom Hearts game available on a Microsoft console.