Place the mirin, sugar and spices into a pan and bring to the boil. Cook over a medium heat for 4-5 minutes, or until the mixture reaches a syrupy consistency, then add the chopped plums and remove from the heat. Mix well to evenly coat the plums in the sauce.
Brush the scallops with the oil and season with salt and freshly ground black pepper. Heat a frying pan until smoking, then sear the scallops for about 30 seconds on both sides, or until golden-brown all over.
To serve, spoon a little of the plum sauce into the bottom of four serving bowls and place a scallop on top of each bowl. Scatter over the nori pieces and chives.
