The primary ingredient in Japanese miso soup is miso paste, which is made from fermented soybeans, salt, and a specific mold called "koji." This ingredient gives the soup its characteristic umami flavor. Miso soup is often prepared using dashi, a flavorful broth made from kelp and fish flakes, which serves as the base. Additional ingredients may include tofu, seaweed, green onions, and sometimes vegetables, depending on regional variations and personal preferences. Miso soup is a staple in Japanese cuisine, commonly served alongside rice and other dishes, and is appreciated for its versatility and nutritional benefits.