It's less figured out and more that she's encountered this situation before, but close enough, for now. In any case, Ritsuka nods at his reply.

"You're from this world, right? Have you heard about how some people from here have gotten memories of past lives in other worlds?"

A pause, to let him have a chance to actually think about about that before she gets to the main point.

"Because I arrived here from another world, and I knew a version of you there."