This takes some build up.
Kingdom Hearts At Home:
The game starts off with Sora on Destiny Islands, he is finally back home. We finally get to see Sora's Mom.
Sora doesn't realize what his mother went through all these years, her year long memory loss when Sora was sleeping (forgot Sora) and him disappearing. Sora isn't appreciating what his mother does. He plays games on his gummiphone at the dinner table instead of talking to his Mom during dinner.
It's night, Sora is in his room when he sees a bright light outside. His Mom was abducted by aliens. Sora manages to catch a ride on the spaceship.
Eventually, Sora is on a whole other world. He finds out the Aliens - Martians needs Moms.
Mars Needs Moms world
The game also includes worlds based on: Mulan II, Home on the Range, Incredible Hulk (2008), Chicken Little and Cars
Mulan II eh? I think I can make something out of that.
Land of the dragons (The sequel)
Party member: Mulan
Alright, so this movie is bad, really bad. The way that it ends leaves the entire fate of the country in limbo, so that's what KH at home will do as well. It starts off with SDG landing in the bamboo forest like their first visit, and they realize where they are. After walking to the Imperial palace, they see Mulan and Shang escorting the princesses with their horses. Mulan explains to them the importance of this mission which prompts Sora to ponder if his love for Kairi is true or not. While halfway through the journey, Mushu is being a giant prick (I mean, trying to uphold the family honor) and tries to break up Mulan and Shang, with some help from SDG, because it's bad enough the dragon's a jerk, why not our likeable protagonist. Eventually this leads to a Li Shang boss fight because of Maleficent corrupting his conflicted feelings, with him making this face the whole fight.

(He's not a hard fight, by any means. If the cloaked figure that arrived in the second visit can beat him, there's no reason why Sora can't put him in his place. If you lose to this guy, I lose respect for you).
This fight takes place near the river and he falls off just like the movie. Mulan's princesses that she escorts still fall in love with the comedic relief, and then the climax has SDG trying to stop Mulan from going through with the political marriage, only for a giant heartless to corrupt the statue that Mushu uses in the movie, leading to another dragon fight in front of a royal palace.
Eventually, the conflict is resolved, Li Shang is alive and well, and everything turns out okay, until the fire nation attacks.
(I mean, the huns, yeah, the huns, that's what I meant to say).