Rinse Rice: Gently rinse Calrose rice under cold water. Drain very well.
Pressure Cook Calrose Rice: Place 2 cups (470g) medium grain Calrose rice and 2 cups cold water in Instant Pot Pressure Cooker. Close lid and pressure cook at High Pressure for 6 minutes. Turn off the heat and Full Natural Release (roughly 10 mins). Open the lid carefully. Fluff and set aside to cool to touch.
Create Spam Musubi Sauce: While the rice is pressure cooking, mix 2 tbsp Japanese soy sauce, 2 tbsp granulated sugar, and (optional) 2 tbsp mirin together in a glass measuring cup.
Cut Nori: Cut 3 pieces of Nori into 8 - 9 long strips.
Prepare Spam: Open a can of spam, cut spam into 7 - 10 pieces. Wash & set the can aside as we will use it as a mold.
Brown Spam Slices: In a medium heat skillet, brown each side of the spam pieces for 1 - 2 minutes. Brush sauce mixture onto each side of the spam pieces and caramelize for 10 - 20 seconds per side. Set aside on a plate.
Create Spam Musubi: Place a piece of plastic food wrap in the spam can. Pack portions of cooked Calrose rice in the spam can and cover the rice with food wrap. Use your fingers to tightly press down the rice. Remove wrapped rice from the spam can by pulling the food wrap upwards. Unwrap the rice and add a layer of Furikake.Place a piece of browned spam slice on top of the rice and wrap a piece of nori around the rice. Use a few grains of rice as glue to seal the ends if necessary.