Bring water and butter to a boil in a saucepan; remove from the heat and stir in couscous. Cover and let stand for 10 minutes, then fluff with a fork. Transfer couscous to a bowl and allow to cool, 5 to 10 minutes.
Stir persimmons, apple, mandarin oranges, and 3 tablespoons reserved mandarin orange liquid into couscous; mix in honey. Stir walnuts and cinnamon into couscous; toss well.