For Beijing, scallops have served as a diplomatic pressure point. For Japan’s allies, consuming them is portrayed as an act of defiance against what they characterize as economic coercion. For Tokyo, the mollusks have become a case study in the difficult — and perhaps increasingly necessary — task of curbing its reliance on China.

Beijing is courting Seoul on key regional issues just ahead of South Korean President Lee Jae Myung’s inaugural state visit to meet Chinese leader Xi Jinping, a trip that comes as tensions simmer between China,