"Oh, it does get completely dark in this void," Nita replies.

"So it's... both true and not, in that case?"

What little Nita has heard about Duels is easy to explain:

"Some of the people who arrived here a while back - either when I did or shortly thereafter - knew what duels were and put on one for the train at large. Even showed us how to make our own decks, after. Shadows weren't all that relevant, but one of them did mention a 'Heart of the Cards'; was that related?"

Not mentioning what Wester had gotten up to - given Nita hadn't even been on the train for that, it seemed in poor taste.