Images reveal that Ralph from the movie Wreck-it-Ralph will be in the KH3, as well as the Fix-it-Felix Jr. game shown on the same movie. This is all happening while Sora and the gang is in the Toy Story “world.”
Theory time! It might be a stretch to say this, but, I will put in my two cents that Ralph is part of a “lost world” in the KH series. He and the game Fix-it-Felix Jr. might be the only ones left in their world consumed by darkness, and now, he’s trying to bring the “game world” back to where it is supposed to be.
On a contrasting theory that I also have, Ralph may be a denizen of a “new world” that was birthed due to the balance of light and darkness being thrown apart. And apparently, he went out to another related world, the world of Toy Story, as when he was looking for a way to be a “hero” (major plot point of the movie). He might accidentally stumbled on a “Door to the Heart of the World” and arrived on the closest connecting world, and found Sora, Goofy, Donald, Buzz, and Woody. Again, these are only possible theories as to why Ralph is in the game.
Might he possibly be a story-related character? Will this appearance mark a new summon for Sora? Who knows! Maybe you have an idea and would want to share it to us down on the comments below.