Rinse the Calrose rice and cook according to package directions, typically on medium heat for about 20 minutes.

In a saucepan, combine dark brown sugar, soy sauce, mirin, and sesame oil. Stir over medium heat until sugar dissolves.

Slice Spam into even pieces and pan-fry until golden brown. Coat with teriyaki sauce and cook for a few more minutes.

Layer cooked rice in a musubi mold, add furikake, then pour in glazed Spam. Compress well.

Wrap with nori, sealing tightly, and moisten the edge with water.

Slice the Spam Musubi into bite-sized pieces and serve warm or at room temperature.