19th Century photograph of men wearing mino straw raincoats
There were a variety of raincoats, jackets and capes worn to protect one from the elements during the Sengoku Period and early Edo Periods of Japan. The shinobi would utilize these to change their appearance and body shape and to stay warm in harsh climates. There were mino (蓑), raincoats made out of straw, gappa travel capes and dôbuku, which were large broad-sleeved coats. There were also the happi (法被, 半被) and haori kimono-like coats. Kimonos were very common and would have been worn by shinobi.
The Shoninki shinobi manual recommends wearing a long haori (羽織) jacket or a rain cape. A raincoat called amabaori is mentioned in the text and how it could be used to change one's appearance and body shape. The same could be done with a cape or raincoat.
The Giyoshu military manual describes a shoulder-length raincoat made with oiled paper designed like a chohan-zukin hood with a cord to carry around.