I re-handled a Kikuichi TKC this week that showed me a problem that I wanted to bring to people's attention so that you can address the issue for yourselves.When I pulled the scales off I was shocked by the amount of rust on the tang, easily 4 times the worst I've seen. What stuck out was that there was more at the bolster than at the ass end.
I went to cleaning the rust out and squared off the inside corners (bolster to tang unions) and then I noticed that the bolster wasn't welded on - it's pinned on and it looked like it had slight gaps.
I decided to take preventive measures and seal the bolster seams with CA glue. What happened next is what brings this post. The CA glue ran down from the top of the bolster (to tang joint/seam) and flowed out down between the bolster and tang - the exact spot where all the rust had built up under the scales. This clearly showed me that these seams were leaking water through from the outside and down under the scales rusting the handle from the inside out.
I eventually poured enough CA glue into the seams (from all directions) to stop the flow and seal it up nice. I would suggest that owner's of these knives do the same thing although I'm sure that the rust (if it's going to happen) already has so I don't know if this will help or not.
Why is this worse on this knife than others? Usually bolsters are welded on and ground smooth - no seams at all. In the west we pin bolsters on just like this knife has however they're always sealed with either solder or epoxy. There are some Japanese knives (like the Hattori KD) that uses pins but they're fit up must be a lot better than what Kikuichi does on this knife.
Funny thing about this is that only a few of the Japanese knives use epoxy under the scales and yes they do rust a bit but nothing like the rust coming out from under the bolster on this knife. Maybe the steel type used in the bolster is having an effect on this? Who knows.
Maybe this one knife is an exception - maybe a bad fit on just this one, I'm not ready to condemn them all for having this problem, but if I had one in my kit I'd take a look at it and maybe even seal it up too, it can't hurt.