Maybe it was this?
Nori, a dried seaweed resembling sheets of black paper, is a very popular ingredient in Japan, particularly for the wrapping of steamed rice to make maki-zushi (rolled sushi) and onigiri (rice balls). Nori is an ideal food for those whose lungs have been damaged by smoking as it can help prevent tar attaching itself to the lungs. It is also said to prevent anaemia, hair loss and greying. It is rich in vitamin B1, which helps combat mental fatigue, and calcium. Seasoned nori is also popular.