Since the game is leaking anyway and I got word that S-E is going to take action next week, here you have. This is, of course, all fake information that won't get proved right in exactly one month.
> worlds
all disney worlds have been shown already. mysterious tower and twilight town are not the same location this time. radiant garden, castle oblivion and keyblade graveyard are in but like mysterious tower, they are pretty small and not fully fledged worlds.
> playable characters
sora and riku, no third playable character. the twist is that the game makes it seem controling riku will be a one time thing but you regain control later at the end.
> final fantasy characters
squall and rinoa get scenes in radiant garden, kid noctis gets a short appearance (he has lost his friends and follows sora, donald and goofy thinking they were the three lost heroes). everyone else "busy" with the city restoration program.
> story
beginning picks up directly after 0.2, sora goes to hercules to regain his lost strength but the world gets attacked by the organization, hades teams up with maleficent and they unleash the titants. then sora gets his clothes at mysterious tower and is tasked by yen sid by finding the key to return the lost friends, while riku must find the bbs trio, yen sid reminds them that their mission is urgent since if they don't find the seven guardians in good form, xehanort will go after the princesses of heart, so sora must travel to the disney worlds avoiding that while he finds out the key
> axel and kairi
their mission is to train for the xehanort fight so they don't meet sora and riku. their scenes are isolated from the rest of the story. kairi has namine's painting book
> organization xiii
master xehanort, young xehanort, ansem, xemnas, terra, vanitas, xigbar, saix, demyx, luxord, vexen, marluxia and laxerne. these last two leave midway and are replaced by fake riku and xion
> the key to return hearts
sora is asked by yen sid to search for this key, and the twist is that it's not an actual keyblade but the ability to heal the pain of a suffering heart that is connected to yours. it's explained that sora already used this key with ventus in bbs. sora returns ventus heart in castle oblivion while laxerne, vanitas and aqua fight
> connection to kingdom hearts mobile
after marluxia reveals himself to sora in tangled, he gets wounded by the battle against the heroes. he flees to keyblade graveyard but is met with just xigbar, which reveals that he is following xehanort's steps since he is connected to a lost master called luxu. before kh1, xigbar recruited marluxia since his true goal was to take revenge for the missing dandelions. it's implied a fallout by the union leaders. xigbar informed marluxia and laxerne about xemnas past and the events of bbs and the two of them wanted to find ventus for revenge. it's revealed that xigbar had a twin brother and they both wore the same robes at one point, mischeiving against the rest thanks to the book of prophecies. xigbar kills marluxia. laxerne flees.
> maleficent
she's looking for the black box and xehanort's keyblade, she travels the worlds in order to gain a piece of xehanort's heart for herself in order to access the keyblade. she still has the ability to control heartless. by gathering the princesses of heart, she believes to be in a position to negotiate with master xehanort
> roxas
as hinted to ienzo by king ansem, sora gets to twilight town in virtual mode in order to return roxas heart to a vessel made of data, however the capsule opens and it's empty. they lose hope of seeing roxas again and during the final battle, it's revealed that roxas had already returned by himself when riku restored sora's heart in dream drop distance
> scala ad caelum
xehanort and sora are the last ones standing after the keyblade graveyard battle, the chi blade is forged by the clash and xehanort claims kingdom hearts for himself by using the power of his other selves and offering the six guardians of light as a counterpart. with the power to create a new balance between darkness and light, he recreates the land of the lost masters, scala ad caelum, sora travels there. after meeting everyone again at scala ad caelum and they defeat master xehanort, he opens the gate to kingdom hearts and flees there, the heroes follow him and end up in literal shinjuku
(the tower on the right is an actual building in shinjuku)
> kingdom hearts
the world logo is kh1's title card but it becomes corrupted and it is revealed as the radiant city asleep in the shadows or something like that. hooded figure carrying the black box appears and reveals himself as ephemer. he recognizes xehanot's keyblade and summons his keyblade to battle him, but it's defeated and master xehanort steals the box, which contains a second kingdom hearts living inside a human heart
Spoiler