For sauce, in a small bowl combine plum sauce, orange juice, the 1/4 cup orange marmalade, tapioca, and anise seeds. Place chicken in a 3-1/2- or 4-quart slow cooker. Pour sauce over chicken.
Cover; cook on low-heat setting for 5 to 6 hours or on high-heat setting for 2-1/2 to 3 hours. Remove chicken; keep warm. Skim fat from sauce.
In a medium saucepan bring water and the 1 tablespoon orange marmalade to boiling; remove from heat. Stir in couscous and salt. Cover; let stand for 5 minutes. Fluff couscous with a fork just before serving. Serve chicken and sauce with couscous. If desired, garnish chicken with orange peel strips and couscous with orange slices.