In a small pot, combine 3 tablespoons of mirin, 3 tablespoons of sake, 1 tablespoon of sugar, and 2 tablespoons of miso paste. Whisk until smooth, then simmer for 3-4 minutes. Set aside to cool.

Place salmon filets in a glass dish and pour the cooled marinade over the salmon, ensuring it's fully submerged. Cover with parchment paper.

Cover the dish with plastic wrap and refrigerate. Marinate for at least 4 hours or up to 3 days.

Preheat your air fryer to 400°F (200°C) or oven to 425°F (220°C).

Remove salmon from the marinade and air fry for about 12 minutes until it flakes easily with a fork.

If baking, place salmon skin-side down on parchment-lined baking sheet and bake for 10-12 minutes until opaque.

Remove from heat, let rest for a minute, and serve with steamed rice and pickled vegetables.