It can be pretty complicated, but once you know it, you remember it easily~ [At least he's not trying to deny it's complicated, but hey, games like that always are. He seems pretty happy at the chance to talk about it, though, even if there's something a little pensive deeper in his expression as well.]

It's called Cardfight Vanguard, or just Vanguard for short. [He seems to consider for a few moments, then starts patting down his jacket as if he's forgotten where something is. Eventually, he pulls out some kind of hard rectangular case in a colour that runs the line between dark pink and red, and pulls out a deck of cards with a practiced hand so he can show the top one to Juno. The actual text is in Japanese even if the workings of the Natha likely mean it's still readable, but that...sure is a lot of text and stats, over a quite detailed picture of a sword-wielding knight in pointed black and red armour.]

There's a lot of variety in the cards, so people can easily make a deck that suits them. That's why it's so popular.