Before fans jump in to "Kingdom Hearts 3," game co-director Tai Yasue suggests that gamers play "Kingdom Hearts 2.8 Final Chapter Prologue" first.

Yasue said that in the world of "Kingdom Hearts" is a "complex story with a lot of threads." The upcoming game will not be an exception.

Speaking to GameSpot, the "Kingdom Hearts 3" director said that the prologue is considered necessary especially for fans to learn more about Aqua, who is trapped in the Dark World connected to Birth by Sleep.

"You experience her sorrow and torment. And she's a Keyblade Master, and her destiny is really intertwined with Sora's in Kingdom Hearts 3," Yasue said.

"So learning about her adventure, and her pain, really gives meaning to when you start Kingdom Hearts 3," the game director went on to say.

As for the worlds to be featured in "Kingdom Hearts 3," fans can expect Disney worlds only. "Final Fantasy" realms will be skipped for now, despite the franchise often being featured in "Kingdom Hearts."

"At this moment, we are not really coming up with any plans for that, we're making original worlds and Disney worlds," Yasue explained in a separate GameSpot interview.

It remains to be seen why "Kingdom Hearts 3" won't feature "Final Fantasy 15," but the even bigger question is which Disney worlds will actually be in the game.

There have been a lot of theories, discussions and wish lists. Yasue, however, hinted that they want those realms that are recognized and "famous," but also "distant and unique."

He did not offer any more clues on the specific worlds coming to "Kingdom Hearts 3," but the likes of "Big Hero 6" and "Tangled" as well as "Toy Story 2" and "Frozen" are being rumored. The worlds of Marvel and "Star Wars" are expected to make an appearance too.

"Kingdom Hearts 3" has no launch date yet, but fans can start digging into "Kingdom Hearts 2.8 Final Chapter Prologue" this December.