Add the cooking sake and pitted pickled plums to a pan. Bring to the boil over a high heat, when it reaches a simmer turn down low and simmer for 10 minutes. Strain the liquid and leave to one side.
Cut the chives into even 4-5cm lengths.
Arrange the sea bream and chives on a plate, drizzling the sea bream with a little bit of the ponzu citrus juice. Serve the plum sauce on the side.