What your hat says - the Kabuto 兜, 冑, samurai helmets

 

The kabuto, the military helmet of the samurai, first appeared in the tenth century Heian period along with the development of the ō-yoroi, the body armor worn by members of the samurai class, although examples of helmets based on Chinese and Korean designs have been found in Japanese tombs dating to the fifth century. Later, in the Sengoku period - 1467-1615 - when warfare saw the introduction of firepower and frequent large-scale battles, a different style of armor, lighter and more protective, came into fashion - the tosei-gusoku - and the style of kabuto changed greatly.

The basic structure of the kabuto was relatively simple - hachi, a metal dome with a cloth lining; shikoro, a suspended neck guard attached at the back and sides; shinobi-no-o, the chin cord, which was often also used to secure the mengu, or facial armor - but the construction and decoration of individual helmets varied considerably.

Most of those included here are examples of the kawari kabuto, or "strange helmet." During the Momoyama period of intense civil warfare - 1568-1600 - kabuto were made to a simpler design, lacking many of the ornamental features of earlier helmets. To offset the plain, utilitarian form of the new helmet, and to provide visibility and presence on the battlefield, armorers began to build fantastical shapes on top of the simple helmets in harikake - papier-mâché mixed with lacquer over a wooden armature - though some were constructed entirely of iron. These shapes referenced forms prevalent in Japanese culture and mythology, including fish and insects, animal ears and horns, grotesque faces, shells, fans, and many other often quite surprising elements. Some forms were realistically rendered, while others took on an abstract, even futuristic feel.

Rear view of the above.