Beyond Kyoukai. [If he's joking about all this, he's very straight-faced about it and shrugs, and after a little pause adds;] The Void sea. It's both a physical sea and a...

[Another pause as Rokuta frowns, waving a hand around in a slow, aimless gesture. He'd said the sea was too large to travel between the two worlds to Kouya, but Kouya had been a child back then... Ragnar was decidedly not that.]

Metaphysical barrier? Crossing between Hourai--- [Snorting softly at himself, he gives an apologetic one-shoulder shrugs.] Japan. This world in general and mine, can't normally be done. So that's where.

[And then, because he can't resist it, Rokuta grins, completely mischievous.]