Remove tough outer green rind from watermelon half using a vegetable peeler; discard. Scoop out red flesh from watermelon using a large spoon, leaving ¼ inch intact where red flesh meets inner white rind. (Discard removed red flesh, or reserve for another use.) Thinly slice white rind with red flesh into 2-inch-long strips (about 5 cups total).
Place sugar, vinegar, water, salt, ginger, and star anise in a large saucepan; bring to a boil over high. Reduce heat to medium, and simmer, stirring occasionally, until salt and sugar dissolve, about 2 minutes. Add watermelon rind strips; simmer 5 minutes over medium. Remove from heat, and let cool in saucepan 30 minutes. (If needed, place a small plate directly on top of rind to keep fully submerged in liquid while cooling.)
Transfer contents of saucepan to a large bowl; place a plate fitted inside bowl on top of rind to keep fully submerged in liquid. Cover bowl with bowl lid, or wrap tightly with plastic wrap. Chill 12 hours before serving. Store, covered, in refrigerator up to 1 week.