Date-maki is an egg dish and eaten especially as one of the Osechi; traditional Japanese New Year foods. The ingredients are eggs, white fish or shrimp paste, fish or kombu kelp broth, sugar and mirin rice wine. These ingredients are mixed and pan fried. Then, rolled by makisu mat.
Due to major New Year food, it can be found easily at supermarkets after Christmas but disappear a few days after New Year's day. Therefore if you want to try Date-maki, you have to be in Japan around New Year's day.
By the way, Date-maki's maki means roll in Japanese but the origin of Date is not clear. One of the origins are from Masamune Date, a famous samurai warlord in late 16th century and Masamune loved Date-maki. Also Date means foppery or dandyism in Japanese. Therefore Date-maki can be translated into foppery roll.