Step 1Grate grapefruit for 2 teaspoons zest; set zest aside. Peel grapefruit, remove sections and set aside.
Step 2Bring grapefruit juice, water, and salt and pepper to taste to boil in covered 9-inch heavy non-aluminum skillet. Reduce heat to medium-low and add fish. Replace lid and simmer 1 minute, then remove skillet from heat and steep swordfish, covered, 6 minutes.
Step 3Pour about 2/3 of cooking liquid into another saucepan. Boil over high heat until reduced by about 2/3. Liquid will become thick and syrupy. Remove from heat, add zest and whisk in butter, 1 tablespoon at a time. Stir in chives.
Step 4Arrange swordfish steaks on platter, pour over sauce and garnish with grapefruit sections. Serve immediately.