Senbei

Senbei (煎餅), alternatively spelled sembei, are a type of Japanese rice crackers. They come in various shapes, sizes, and flavors, usually savory but sometimes sweet.
Senbei are usually cooked by being baked or grilled, traditionally over charcoal. While being prepared they may be brushed with a flavoring sauce, often one made of soy sauce and mirin. They may then be wrapped with a layer of nori. Alternatively they may be flavored with salt or "salad" flavoring, among others.
Sweet senbei (甘味煎餅) came to Japan during the Tang Dynasty, the first recorded usage in 737 AD, and still are very similar to Tang traditional styles, originally often baked in the Kansai area, of which include the traditional "roof tile" senbei. These include ingredients like potato and wheat flour or glutinous rice, and are similar to castella cakes. (Distinctly different from what most people would consider as Senbei today).
Modern senbei versions are very inventive and may include flavorings can which range from kimchi to wasabi to curry to chocolate.