Unroll the Fruit Roll-Ups, leaving paper attached. Cut licorice lengthwise into thin strips; set aside. In a large microwave-safe bowl, combine marshmallows and butter. Microwave, uncovered, on high for 2 minutes or until melted, stirring once a minute. Add cereal; stir to coat.
Place about 1/2 cup cereal mixture on the edge of each roll-up; place licorice in the center of the mixture. Roll up sushi rolls to about 1-inch diameter. Discard paper. Trim edges of rolls; cut each into four pieces. Store in an airtight container.
Packaging idea: Try packaging your "sushi" in a domed container, with a label you design, like this. (We asked to buy a new container at the deli section of the grocery store—the clerk was happy to oblige!)