Rinse the sushi rice in cold water until the water runs clear. Cook according to package instructions (usually 20 minutes in a rice cooker).
Slice the Spam into 6 even slices. In a bowl, mix the soy sauce, brown sugar, and mirin until combined.
Heat a dry non-stick skillet over medium-high heat. Fry the Spam slices for 2-3 minutes per side until golden brown and crispy.
Pour the sauce mixture into the pan with the Spam. Let it bubble and reduce for 1-2 minutes until sticky. Flip to coat the Spam fully. Remove from heat.
Place a Musubi mold (or empty Spam can) on a cutting board. Fill with ½ cup of cooked rice and press down firmly.
Sprinkle Furikake over the pressed rice.
Place a slice of the glazed Spam on top of the Furikake. Lift the mold to release the block.
Lay a strip of nori on a flat surface. Place the rice block on the edge of the nori and roll to wrap the center of the block. Use a grain of rice to seal the edge.