Hideji Suzuki served six years in a Chinese prison on spying charges — a sentence that stemmed, he said, from a dinner party where he did nothing more than try to make small talk with a Chinese academic about North Korea.

Since returning to Japan in October, he has tried to raise the alarm about China’s seemingly arbitrary detentions of Japanese citizens. He is one of 17 Japanese nationals detained on similar charges since 2015, but the only one to speak out about his experience and what he describes as Japan’s weak efforts to help him. His goal, he said, is to shame the Japanese government into taking stronger action to aid others who find themselves at Beijing’s mercy.

Now, with the arrest last month in China of a Japanese pharmaceutical executive on espionage charges, Beijing has tested Japan’s resolve once again.