Gather all the ingredients.
Slice the spam into slices that are 1/4 to 1/2 inch thick, based on your preference.
In a mixing bowl, combine corn starch and water to make a corn starch slurry.
In a large skillet over medium heat, mix Japanese sake, soy sauce, grated garlic, and sweetener. Let the sauce come to a gentle boil, then lower the heat to a simmer. Stir in the corn starch slurry and simmer until the sauce thickens, about 1 minute. Set it aside.
In a mixing bowl, combine eggs, dashi, Japanese sake, and sweetener. Use a hand whisk to beat the egg mixture until well combined.
Coat a frying pan with cooking spray oil and place it over medium-low heat. Once the pan is heated, pour in the egg mixture, cover and cook for 2-4 minutes, flip and cook until the eggs are no longer runny.
Use the musubi mold to punch out 4 egg rectangles and set them aside. You can serve the remaining eggs on the side or discard them.
In a clean, large skillet, heat some cooking oil. Once the oil is hot, add the sliced spam. Cook the spam over medium heat for 2-3 minutes on each side until browned. Place the cooked spam on a plate and set it aside.
Place seaweed strips cut to 1 inch thickness on a flat surface. Position the musubi mold in the center and add 1/2 cup of rice into the mold, pressing it flat with the mold press before removing it. Place the egg on top, brush with musubi sauce, and add the seared spam on top.
At the top of the seaweed, place a few grains of rice in a line to act as glue. Fold the bottom of the seaweed up and over the spam, then fold the top down, using the rice to hold the seaweed in place. Repeat these steps for the rest of the musubi.