There are a few English language books on tenkara that I suggest to my friends and this is one of them. Morgan Lyle has written a great book on simple and effective flies that work for tenkara; and fly fisher for that matter.
I won't go into details, but I will say that this is not a simple as in dumb book, no, quite the opposite. Simple as in very effective but easy to tie. In addition to the patterns, there are stories that tie it all together.
I suggest this book for your library.