My general rule is the harder the steel used in the knife, the smother the rod you should use. The reason for this is that soft steel is unually tough and can be ground easily with a rougher steel rod. You can "sharpen" a soft blade with a coarser rod. With hard steel blades the steel on the edge chips much more easily. So, if you use a rod with grooves you will often just micro chip the edge. So, use a smooth rod and that will touch up your edge without chipping it. Try the F Dick polish steel or the Mac Black ceramic rod. These are both in stock and will work well for your Moritaka. Better yet, strop your knives with some leather or balsa loaded with boron carbide. Strops are gentle on your edges and that's what I use at home. If you work with your knives strops are a little messy and not as convenient so stick with a rod.
Here are the items I just listed:
F Dick Polish steel: http://www.chefknivestogo.com/fdidi12posto.html
Mac Black Ceramic Rod: http://www.chefknivestogo.com/mac-black ... g-rod.html