Because the author wants to build up the suspense, he'll probably show up at the last moment. It's so fucking cliche. But that's how this story goes, I mean look at how long he's kept up the disguise. He may be a badass in fighting, but he's a puss where it counts. I see no reason for him to even disguise himself to begin with.
This is not an omake, this is an actual chapter of the main story. It explains why he can´t use touki, which will limit his performance in battle in the future and force him to take mesures to fix that problem.