As the title says, were shields ever used in Japan? (All periods before the implementation of gun powder) If not, then how come?
You may find some of these archived questions interesting:
Is it true that there were no shields in Japan during the Samurai and in that case why?
Why aren't shields prevalent in Feudal Japanese armies?
Also, search the archives for Japan, Samurai, and shields and you'll find many more threads on this topic.