Tenkara flies are an enigma. Wide variations in Japanese regional tenkara fly patterns exist, yet a few tenkara anglers in Japan use just one fly pattern. At first glance it makes no sense. Upon further reflection it actually makes perfect sense.
Tenkara flies do not attempt to match a specific insect so there is no need to change flies as hatches change. Fish seem to be much less selective when taking wet flies than they are when taking dries. It is important to note also that the high gradient mountain streams on which tenkara developed are not very fertile and do not have the prolific insect hatches. The fish that live there cannot afford to be overly selective.
Very informative overview article on tenkara flies, along with step-by-step guides for tying some of the most popular tenkara flies.0