Judai Yuki... no. The name doesn't ring a bell. There's only a very small handful of duelists I haven't met, but I've never heard his name brought up.

[ And whoever this person is, is either very important to Jun or some sort of enemy. It's not really her business either way, but she's hoping this person he's talking about is more on the friendly side for his sake. ]

If I do see or hear about him, though, I'll definitely let you know.