Prepare the teriyaki sauce by mixing soy sauce, mirin, sugar, and a pinch of pepper.

Clean the mackerel under running water or rice water, then pat dry with a kitchen towel.

Grill the mackerel in a pan without oil until both sides are golden brown.

Brush the teriyaki sauce onto the grilled mackerel and cook on low heat until the sauce is absorbed.

Flip the mackerel once during cooking to ensure even coating of the sauce.