I'm not sure. It'd be better if there were just a way to... portal between the different worlds but, s'far as I know, there isn't.

[He thought a moment, then dug into his pocket, pulling out his D-Stream.] Back home, I was doing my own thing when I suddenly felt this in my pocket, almost like it slid in on its own. And when I looked at it... I remembered.

Now, I'm not saying I secretly had it all along and then it just popped up. It's more like it manifested itself. But it showed that they can exist outside this world. Just need to figure out a way to keep it with us.