I realized that they send in the Replica for Roxas to the Keyblade Graveyard in KH3 the same way King Mickey arrives in The World That Never Was in DDD. Here's King Mickey arriving in The World That Never Was in Kingdom Hearts 3D: Dream Drop Distance. Here's the Replica for Roxas being sent to the Keyblade Graveyard by Ienzo, Even, Ansem the Wise, etc. in Kingdom Hearts III. (Which Roxas' heart comes out of Sora and then goes into the moment it arrives.) It's the exact same method of travel/arriving at a world. They have the same animation of a sparkle in the sky and then a beam of light coming down from where the sparkle was, transporting a person or object to a world.