excuse the journal, too lazy to swap for just OOC talk! haha

From my perspective, I think Killua only seeing him when using Gyo would make the most sense at least. Whether that's only an outline or the full body, I'd say is up to you/your cast.

I'd love to talk it over more, though! I figure it would have to be consistent across the cast, and I don't want to step on anybody's toes by assuming he can or can't see them. At the same time, it actually sounds like a fun thing to figure out.