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What documentation that might exist would be held by the private schools in the form of scrolls, the contents of which would only be revealed to trusted trainees of the particular school. Today, there are many and diverse types of shuriken, which suggests that the advancement of the art was rather fragmented and insular amongst numerous schools and areas.
Chikatoshi Someya Sensei attempted to form some sort of categorization of shuriken in his book "Shuriken Giho", however admitted that without historical records, such categorization is simply speculative, and that there were a number of examples that could not fit in his classification method too. Nevertheless, such categorization can be beneficial today for the function of explaining and discussing the art and the products in usage.
The art appeared to have lost popularity and almost passed away out in the duration right away after the 2nd world war. Numerous masters of the martial arts did not return from the war, as Mr Shirakami states, just three of master Kanji Naruse's trainees survived the war; Shirakami Sensei, Isamu Maeda Sensei, and Satoshi Saito Sensei, the present headmaster of Negishi Ryu.
Shirai Ryu would have died out entirely were it not for Satoshi Saito Sensei resurrecting the art and including it into Negishi Ryu practice, and now, students from all over the world see Japan and train in the traditional arts under these masters. Luckily however, The Most Complete Run-Down of shuriken has probably been saved by it's addition as a supplementary weapon within a rather big number of koryu bujutsu arts, or classical martial systems, such as Katori Shinto Ryu, Tatsumi Ryu, Yagyu Shingan Ryu, Kukishinden Ryu, and so on.
However total transmission of a schools curriculum needs many years of devotion and service, and considering that shuriken was thought about to be of somewhat lower importance than other weapons within the curriculum of many schools, it is likely that shuriken jutsu might continue to decrease over time. Despite this, Shuriken jutsu appears to just recently be undergoing rather of an increase in popularity.