@zek777 A fair and realistic point. Although at the same time I believe the anime studio doesn't quite trust koto music enough, either. Neither OP or ED are koto, and I believe little of the background music has been either. I'm sure there was some koto music there, but not much. I'd have also liked to hear longer performances uninterrupted as well. It's kind of weird in my subjective impressions shows like Angel Beats, which aren't about music at all, still seem to be more music heavy than some anime that are supposed to be all about music/bands, but end up featuring lots and lots of drama, comedy, slife of life, etc instead.
@Kag5n Yeah, I have seen people refer to those before, but I always felt they would be kind of external. I've watched some koto videos over the years, even before this manga started, so it's not like the instrument and style would have been totally unknown to me. It'd just be a different thing to grow to like the characters and then hear them develop and play, even if it's all fiction, as opposed to listening to random real people play the music. That's why I set myself up for a disappointment with the anime.