Regulus tries to hide his reactions behind what remains of his arrogance, still having some trouble concentrating. The talk of multiple universes makes no sense, but he tries to puzzle the rest out despite that. "So, it was an accident..."

"Your arrival in the Nexus? It could have been, Mikoto says. "I have also heard the theory that the place intentionally pulls in people who for one reason or another need to leave their world of origin."

Regulus has to admit, at least to himself, that that would fit... and then it lets him put that talk of 'dimensions' into perspective. He'd... left the whole world? And he had a feeling they didn't just mean the Wizarding World, but all of it... not that he cared much for the muggle side of things.