New Delhi, Feb. 11 -- A photo last month of Japanese Prime Minister Sanae Takaichi wearing a bright electric blue outfit and playing the drums alongside Korean President Lee Jae Myung is only one of many of Japan's prime minister to go viral. The image is also remarkable because Korea and Japan have long had a strained relationship. The camaraderie between the two leaders playing a K-pop song radiated out of the photograph in a manner akin to speech balloons. Takaichi's hands were above her shoulders, as if she had just won a 100-metre sprint.

In a sense, the Japanese prime minister has. As the victor of an internal party vote to become prime minister in October, Takaichi lacked a popular mandate and was momentarily enfeebled further whe...