Clean and prep the salmon, then cut it into bite-sized pieces.
Make the marinade sauce with soy sauce, water, mirin, sugar, minced garlic, and pepper.
Boil the marinade sauce, then let it cool down.
Place the prepared salmon in a container and pour the cooled marinade sauce over it.
Refrigerate and marinate for 4-6 hours.
Serve the marinated salmon in a bowl to finish.