Mix sugar with soy sauce.
Slice your can of Spam into eight or more slices. Pan-fry in a nonstick skillet for about 2-3 minutes until it starts to brown. Flip the Spam and drizzle soy sauce-sugar mixture on top. Continue to pan-fry until it reaches your desired level of caramelization and crispness.
Place a sheet of nori on a prep board and place your Spam musubi maker on top. (If you don't have a Spam musubi mold, simply shape the rice by hand into oblongs, top with shiso leaf and Spam, and wrap with a sheet or thin strip of nori, depending on how you want your Spam musubi to look and taste.
Fill your mold with rice and press firmly with musubi mold lid. This is important - if you don't pack the rice firmly enough, your musubi will fall apart. Add more rice and pack until the mold is about 1/3 full.
Sprinkle rice with furikake and shichimi togarashi and top with Spam slices in a single layer. Add shiso leaves in a single layer. Finally, top with more rice and press firmly.
Remove musubi from mold and wrap with overhanging nori. Slice and eat.