I used to have a Kyocera ceramic kitchen knife. Likely not as hard as that but close I'd wager. Kyocera only recommended one method of sharpening...send it in to Kyocera.

The issue isn't just that the stone needs to be harder than the blade...if the stone is too coarse, you can easily chip the blade badly. Finishing stones should be good but I'd expect to need to put a ton of elbow grease in.

FYI. I know how easy it was to chip because my wife used it ONCE and it was jagged as a saw blade just from her banging it around in the sink with some dirty dishes to wash it off. Kyocera wouldn't sharpen it for free because it had been mistreated.