I assume that you are asking about the samurai, who were the class of Japanese warriors similar to the knights of medieval Europe.

If this is the type of Japanese warrior you are asking about, the most important thing that they wore in battle was full suits of armor.  This armor could be made from leather or from iron.  These suits of armor covered the samurai from head to toe.

The major parts of the armor included a helmet, breast plates, shoulder protection, long glove or sleeve like armor to protect the arm, thigh and shin guards.  Follow the link below for a much more detailed discussion of samurai armor with illustrations.

What did medieval Japanese clans wear?

Japanese clothing was unique because of its production method and that fashions were unisex. During the Asuka period when the Soga clan was in power the kimono was introduced as the de facto clothing among men, women and children. Although both genders wore kimonos, there were slight differences between males and females. For example, the obis (wide sash) was worn exclusively by women and complemented with an elaborately ties bow. Most clans, especially those with close imperial ties, wore kimonos of silk rather than those made from cotton or hemp. Kimonos were generally decorated with wood block printing methods.

Some members of the samurai class wore a different outfit called a hakama, which was like a shirt rather than a robe. Samurai also favored baggy pants which allowed for greater movement. It was not uncommon for samurai from a specific clan to wear the seal of their particular clan or wear clothing with a clan-specific color.