Old wakizashi signature help

I've been obsessed with Japanese swords for almost fifty years, but never thought I would own one. I was given an old wakizashi a while back--probably almost twenty years ago. I believe the person who gave it to me purchased it at a Christie's auction, but unfortunately he copied the wrong page out of the auction catalog, and I have no way to ever get any questions answered. The tang only has markings on one side. I'm uploading pictures with different angles of lighting, hoping to get some help with identification. Here's all I could come up with:
The first two look like Hoshū, so Buzen or Bungo.
The third looks like Jū, so 'resident' or 'dwelling'.
Can't find anything on the fourth or fifth characters.
Later, I may ask advice on the saya, which is not in good shape and is missing the tsuba. But for now I just want to know about the blade.