But here's my problem with the hypothesis that the Bujinkan got their techs from pirates: it creates more problems for explanation than it solves. Sure, there were pirates all over the South China Sea, the Sea of Japan and the open north Pacific. Yes, they put into port in Japan. But they also put into port in Korea, China, Okinawa, Indonesia and all kinds of places. Would we not conclude, on the basis of the same reasoning as the OP, that there may/must have been substantial transmission of techniques to these places too?? And just looking at Japan: why was it just the Bujinkan that got its techs from the pirates?? The communities typically associated with the ninja professions were not the most obvious ports of call for pirates; in fact, they were notoriously inaccessible. Wouldn't we expect to find the pirate arts, whatever they were, much more abundantly represented in places where pirates themselve were much more likely to frequent, such as the main southern coastal ports? In other words, why would pirate arts only show up in the Bujinkan, when the Wokou and other pirates were familiar visitors up and down the Japanese coast????