Even as Japan’s prickly territorial disputes gained heat in recent months few well-known figures outside of political circles have taken a stand on the touchy issue that has sparked trouble across business, sports and cultural spheres. But on Friday morning, Japan’s best-known living author joined the war of words.

Novelist Haruki Murakami penned an essay expressing his concerns about the cultural fallout that is likely to result from the country’s various escalating territorial spats and described the feverish reaction to...