Cook rice. Rinse the rice with cold water until it runs clear. Cook in a rice cooker, following the manufacturer's instructions. Transfer cooked rice to a large shallow bowl and cool briefly.
Slice Spam. Slice Spam into 6 thick slices, about 1/4-inch thick. For one can of Spam, that makes 6 portions.
Cook Spam. Heat a non-stick skillet over medium heat. Add the Spam slices and cook until lightly browned, about 2-3 minutes per side. *There's no need to add oil, as the Spam slices will release oil as it cooks.
Make glaze. While the Spam cooks, make the soy sauce glaze. In a small bowl, add soy sauce, sugar, mirin, and water. Stir well until the sugar dissolves. Set aside.
Add glaze. When the Spam has turned golden brown on both sides, add the glaze to the pan. Cook until the Spam absorbs the glaze. The sauce will reduce and become thick and syrupy. It should coat the Spam slices. *Add a little water if it reduces too much.
Shape rice patties. In the large shallow bowl, divide the rice into 6 equal portions with the rice paddle. Shape the rice into patties. Use a musubi mold, an empty Spam container, or your hands. Dip clean hands into cold water to prevent the rice from sticking too much. Or, use food preparation gloves.
Cut Nori. Use clean kitchen scissors to cut 3 Nori sheets in half cross-wise. You should have 6 half sheets of Nori. Set aside.
Assemble. Add a sprinkle of furikake on top of each rice block. Then, add a glazed Spam slice on top. Wrap with a nori sheet, shiny side up (rough side touching the spam and rice). Repeat until all Musubi are assembled.
Serve. Transfer to a plate and serve immediately. Or, wrap Spam Musubi individually in plastic wrap for later eating. Enjoy!