He could ask - it's not as though Yaeko's going to judge someone for being weird.

"They're a bit more solid than ghosts are purported to be, but essentially, yes. When I say they lack substance, it's like..." Hmm. This Akira is unlikely to know from video games.

Fortunately, Yaeko has other comparisons to draw from. "Like background characters in a play, or unfocused details in a painting. They aren't there to do anything, really, but take up space and go about their business, because our minds expect those details to be at least somewhat filled in."