I've seen a lot of people say that they think the new secret ending takes place in alternate universe, but I don't. I actually believe that they are in the realm of darkness. Think about it, look at how the place looks after the UEM blasts the sky and how everything looks. Then compare that with the beach scene in the realm of darkness at the end of KH2. So I think that, Mickey's master Yensid starting training Mickey, and gave him the Star Seeker to use (you never see a keychain on the star seeker, granted his body may be blocking it, but still you don't see a keychain on it). When sent to the battlefield, Mickey was too late. And the realm of darkness was taken over by the UEM. It would make sense because Mickey said he found his keyblade in the realm of darkness, and since the 3 knights were defeated the keyblade for that realm would've gone to the one with the strongest heart, which would've been Mickey.
Now I know some people will try and say well what if that place is the realm why would the Sora and Riku's keyblades be there too? Remember this video is different from the secret ending of KH2. In this one you don't see those 3 keyblades at all, which could've been a change he made on purpose, like the changes he made from ASAS to DD. So anything is possible, but the one thing I don't have a comment on is why the other keyblades are there. That detail aside I think it's a pretty solid theory. Let me know what you think, critism is fine but flamming isn't.
Now I know some people will try and say well what if that place is the realm why would the Sora and Riku's keyblades be there too? Remember this video is different from the secret ending of KH2. In this one you don't see those 3 keyblades at all, which could've been a change he made on purpose, like the changes he made from ASAS to DD. So anything is possible, but the one thing I don't have a comment on is why the other keyblades are there. That detail aside I think it's a pretty solid theory. Let me know what you think, critism is fine but flamming isn't.