The title really says it all. I can't recall ever seeing a depiction of a Japanese samurai or ashigaru warrior using a shield in popular media or historical sources. Were they ever used? And if not, why not? It would seem like common sense against arrows, which feudal Japanese armies seemed to make extensive use of.
You might be interested in some threads from the FAQ section on "Ninjas, Samurai, and related errata":
Is it true that there were no shields in Japan during the Samurai and in that case why? - 11 comments, over 2 years old.
A flaired commenter gives a detailed overview of how the combat styles and tactics of Japanese warfare affected shield usage throughout various periods in pre-Modern Japan.
Why were shields so much more prevalent in warfare in Western Eurasia, Africa, and some parts of the Americas than in Chinese and Japanese warfare? - 70 comments, over 2 years old.
This thread delves into a more equipment based analysis to explain mobile shield usage (and lack thereof) in pre-modern Japanese warfare with many followup questions given detailed responses.