I've polished a couple of Shigefusas to a really nice satin finish using 220 wet/dry sandpaper. Put the knife in a knife vise if you have one, put the sandpaper on a sanding block backed by hard rubber (buy one if you don't have one). Lubricate with water with a couple of drops of Dawn added. Polish in one direction only (heel to tip is recommended). Very important: change sanding sheets every time you turn the knife over to work on the other side of the blade. Strive to move the sanding block in a straight line.
I've tried going to 300 and 400 grit, but this starts to give a polished finish, so I always drop back to 220.
Here's a picture of one I just finished:
P.S. I polished the hagane on a Woodcraft buffer, but that's a whole 'nother story.