Sushi Den has a few branches across Bangkok, my favourite is the one in Terminal 21 because its nice and close to my house but they also have branches in Siam Paragon and Central Ladphrao.
They have a range of sushi and sashimi, you can order sets or you can order per piece. Pieces of sushi start from about 30฿ and go up to 200฿. Sets of 6+ pieces start fro 290฿ and go up to 950฿.
Their charred salmon you can see above, is not only the best piece of sushi i’ve ever eaten but actually one of the single best pieces of food i’ve ever eaten, it is definitely foodgasm worthy.