Osato Kotsubu Natto, also known as "Umai Ga Ichiban," is a type of fermented soybean product originating from Mito, Japan. The term "Kotsubu" refers to the small-sized soybeans used in this natto variety. These smaller beans are known for their delicate texture and enhanced flavour profile. Each package of Osato Kotsubu Natto includes a sachet of sauce and mustard. The sauce is a blend of soy sauce, mirin (sweet rice wine), and other seasonings, while the mustard adds a spicy kick to the dish. These condiments complement the rich umami taste of the fermented soybeans, enhancing the overall flavour experience.