Karazuri means 'empty printing'; it consists in carving a pattern into a woodblock and then printing it in the usual way with a baren, but without any pigment being applied to the wood. The pressure of the baren on the back of the paper causes part of the paper to be squeezed between the wood and the baren - and thus flattened. Areas of the paper that remain untouched by the pressure keep their original fullness. It is the difference between these two that gives the embossed appearance. So the 'raised' areas of the block will be pressed into the paper, and the 'carved away' areas will end up forming 'bumps' on the print surface.
Here my paper on this "Inkless Printing"