Short summary.
Keybladers get message that a group of people named the Six Senses are being fuckers and making some fake world thing so they have to go collect some magical maguffins called the Signs of Zodiac to help them locate the fake world they are creating or whatever. So they battle through world after world in KH esque story movies helping the people there, kicking ass, and collecting these McMuffins.
Naturally they work together while doing this.
The group is very dysfunctional and everyone has problems. Lots of drama, in group tension, plotting.
The main party... works... somewhat.
Oh and apparently there is some other super bad enemy organization who thinks they're hot shit or whatever (yea, I said it, deal with it >:3, Lucas and his horseman friends are going down baby) and they hate the Six Senses as well, but like the NPC quest givers in an MMO they are too lazy to go fix their own problems so they are letting the heroes do all the dirty work.
That is about the worst best summary you could possibly get, but it works and I am too lazy to make a full one.