It is most unusual to find a walnut board from japan, so if it isn’t walnut, it is a close cousin.  As the photos of the top show, the depth of the grain patterns changes quite a bit depending on the light and your angle to the board.  (In this respect, it is second only to the “maple” board.)  One end does have a short crack, and the other end appears to have a longer crack.  The short one is open enough to slide a piece of paper into, while the longer one is more visible but closed.  In the years that I have had the board, it has not changed.  All five surfaces are flawless.  153 mm.