"Depends on what exactly you mean by 'realms'," Lea said. "My world has a set up that I've realized is kind of unique. It used to all be one world, like most are, a long time ago, but that world was destroyed in a massive war. What was recreated after it is a lot of smaller worlds that are parts of the old bigger one. The smaller worlds are mostly sealed off from one another, but the inherent connection they still share means that travel between them is difficult, but not impossible if you know how. Most of the smaller worlds aren't even aware of the others' existence though, so the number of people with that know-how is a pretty short list."

"The world 'realm' there specifically describes where these smaller worlds are located. There's three realms: the Realm of Light, the Realm of Darkness, and the Realm Between. The Realm of Light is where most worlds are located and consequently where most people live. The Realm Between is a lot smaller and has a lot fewer worlds; and because it exists between the Realms of Light and Darkness, a lot of the worlds that are there have unique properties. Like for example, there's Traverse Town, a world that only appears when someone is lost or traveling between worlds and needs a refuge. The Realm of Darkness, meanwhile, I already described to you a bit. It doesn't have any proper worlds and it just kinda one big space saturated with darkness where time and space as we know them just don't work right. It's where Heatless come from and no one could really live there. A very weird, icky place."

"So in the context of my own word? Yes, a Keyblade portal or dark corridor could allow someone to travel between realms. But there's a fairly good chance that 'realms' might mean something different in your world."