To make the Sushi Vinegar: Combine red/rice wine vinegar, Mirin, sugar, and Kombu.
In a bowl, mix freshly cooked hot rice with about 2 tbsp of the sushi vinegar mixture and mix well. Cover rice with tea towel and set aside to cool to room temperature.
Lay a nori sheet shiny side down, forming a diamond.
Add about 1/3 cup of sushi rice in the middle, forming a square and leaving space on the sides. Wet hands with water to keep it clean from sticky rice.
Layer a SPAM® Classic slice, egg, and other preferred filling on top of the rice.
Finish with another layer of sushi rice, making sure all the fillings form a square.
Wrap the nori edges around the filling like an envelope then flip upside down. Allow it to rest for about a minute to form shape and firm up.
Slice in half and serve.
Sauce suggestions: Teriyaki sauce, Okonomiyaki sauce, or Japanese mayonnaise.