Do you play from memory much? Most people scowl at the thought. After all,playing even a short song from memory requires more effort. So, we tend to avoid it as players. However, it is certainly impressive from the perspective of the audience to have someone play for you without notation.
You should be able to play some honkyoku, especially, without relying on notation. After all, one meaning of the name "honkyoku" is "your own song". Performing without notation will add a certain tension and intensity that can be lacking if you rely on notation, always relying on which can breed complacency.
Also, playing the song over and over again in the process of memorizing it will help make the song a part of you, so that when you do play it it becomes a natural expression. In other words, playing from memory will give you a different relationship to the song,and show you things you might not have seen.
However, it is undeniable that memorizing an entire song is difficult.Here I will introduce a few techniques (assuming a honkyoku), so experiment and improvise and see which one works best for you.
Look for repeated phrases. Even if they are not identical, you will find many very similar phrases. Label them with A, A', B, B‘, etc. Sometimes just this one step can cover half the piece.
Memorize the phrases immediately before and after phrases which stick out anyway.
Cover the parts you've already memorized with paper.
Mark the prases you will have difficulty remembering. Or, draw a little picture next to it. Anything to make it
Once you‘ve memorized a good chunk of it, try playing through the whole piece. Don‘t stop no matter what.
Try to memorize the piece in as short a time as is realistic (1-2 weeks, for instance). Drawing out the process can actually make it more difficult.
Remember, memorizing honkyoku is not an easy task. The key is concentration. Since it is easier to concentrate in spurts, try to complete the memorization as soon as you can. Don‘t dawdle with it.
If you memorize the piece to the point where you can sing it aloud, you will make very few mistakes in performance. Ideally you should get to the point where the next phrase comes out naturally, without even requiring thought.Singing from memory is a good intermediate step to get to this stage.
So, give it a try. Pick the honkyoku that touches you most deeply and getto the point where you can perform it in front of people with confidence.