Lay your salmon steaks flat and remove the spine by running a knife along one side of the ribs from the top of the salmon to the bottom.
Repeat for the other side, and then discard the bones.
Rub all four pieces of the salmon with the oil, then lightly salt.
If you are using a grill, get it nice and hot. Grill the steaks until they’ve got some good grill marks and no longer stick to the grill (about 3 minutes), then flip and grill until they are almost done (another 2 minutes).
If you are using a broiler, move the oven rack to the top position and preheat it on “broil”. Put a wire rack on a baking sheet and lay the salmon steaks on the rack. Broil on one side until it takes on some color, then flip and broil the second side until the salmon is almost cooked through.
To make the sauce, add the sugar, sake and soy sauce to a frying pan large enough to hold all four pieces of salmon.
Heat over high heat until the bubbles get very large and the mixture is thick.
Add the salmon steaks and coat in the sauce, turning a few times to coat evenly and cook the salmon through.
Serve the salmon teriyaki over hot rice drizzled with the remaining sauce.