Karashi Mentaiko Onigiri is a popular Japanese rice ball dish that is filled with spicy cod roe. The rice is seasoned with a mixture of soy sauce and vinegar, giving it a tangy and savory flavor. The spicy cod roe adds a burst of heat and umami to the dish. Onigiri is a convenient and portable snack that can be enjoyed on the go or as a light meal. It is a favorite among both children and adults in Japan.