For his family’s first overseas trip together, Tang Junjie carefully planned a holiday to Japan during China’s longest Lunar New Year break on record. Flights were booked months in advance by the 22-year-old from Sichuan province, who had already made three solo visits to the neighbouring country that has long been a draw for Chinese tourists. But a sudden deterioration in Sino-Japanese relations changed everything. “The original plan was to transit through Seoul on our way to Japan,” Tang said....