Start by combining soy sauce, water, rice wine, and sugar in a saucepan. Bring it to a gentle boil for about a minute or two, then allow it to cool completely. This ensures your salmon absorbs the flavors without cooking it.
Thinly slice the onion, chili peppers, and lemon. These add subtle aroma, color, and a refreshing bite to the salmon once marinated.
Cut the fresh salmon fillet into 1/4-inch thick pieces, approximately 2–3 inches long. Uniform slices help the marinade penetrate evenly, giving each bite consistent flavor.
Place the salmon in an airtight container and add the onion, chili, and lemon slices. Keep it in the fridge while the marinade cools, preventing the fish from slightly cooking from the heat.
Once cooled, pour the marinade over the salmon and vegetables. Cover tightly and refrigerate. The salmon is ready to enjoy after 4–5 hours, but flavors deepen if eaten the next day. Best consumed within 2 days.