Japanese rice crackers known as senbei are made mainly from rice.
Senbei are a broad family of Japanese crackers whose principal ingredient is rice, commonly Japanese rice such as uruchimai or, for some varieties, glutinous rice. The rice is cooked, shaped into dough or pieces, dried, and then baked, grilled, or fried. Many crackers are brushed with soy sauce and mirin, seasoned with salt, or wrapped in nori seaweed.
Senbei have a long history in Japan. Sweet versions were influenced by foods arriving from Tang-dynasty China, with a recorded Japanese use of the term dating to 737 AD. The salty, soy-seasoned style familiar today became especially popular during the Edo period, including through teahouses in Sōka. Sōka senbei remains strongly associated with Sōka City in Saitama Prefecture.
Rice is the defining grain, but not every cracker sold under a senbei-related name is rice-only. Some regional varieties use wheat flour or starch; Nanbu senbei, for example, is made with wheat flour. That exception does not change the standard answer: senbei are principally recognized as Japanese rice crackers.