The story
From the appearance of an uncut roll, in which the tail of the piece of prawn tempura protrudes from one end, resembling the fuse of a stick of dynamite.
Etymology from Wiktionary, CC BY-SA 4.0.
dynamite roll
Today it means: A type of Western-style sushi usually containing a piece of prawn tempura and capelin roe with vegetables and Japanese mayonnaise. Full definition →