In an opinion piece published in Britain's Daily Telegraph newspaper on Monday, Tokyo's envoy to London, Keiichi Hayashi, compared Beijing to the villain of JK Rowling's books.
"East Asia is now at a crossroads. There are two paths open to China," he wrote.
"One is to seek dialogue, and abide by the rule of law. The other is to play the role of Voldemort in the region by letting loose the evil of an arms race and escalation of tensions, although Japan will not escalate the situation from its side.
"The answer seems obvious. Although China has so far refused to enable dialogue between our leaders, I sincerely hope that it will come forward, rather than keep invoking the ghost of 'militarism' of seven decades ago, which no longer exists."
Asia's two biggest economies have a difficult relationship characterised by disagreements on a wide range of issues, many of which are tied to memories of violence in Asia by Japanese soldiers before and during World War II.
Things have worsened since Tokyo claimed a set of disputed islands in East China Sea in 2012, fuelling nationalism in both nations and naval and air force stand-offs around the isles.
Hayashi's letter was an apparent response to an earlier op-ed, also invoking Voldemort, published by the paper on January 1 by Liu Xiaoming, Chinese ambassador to London.
In the letter, Liu criticised Japanese Prime Minister Shinzo Abe's recent visit to Tokyo's Yasukuni war shrine, which honours Japanese war dead, including men convicted of war crimes after Japan's defeat in 1945.
The shinto shrine is seen by China and other Asian nations as a symbol of Japan's militarist past.
"If militarism is like the haunting Voldemort of Japan, the Yasukuni Shrine in Tokyo is a kind of horcrux, representing the darkest parts of that nation's soul," the Chinese envoy wrote.
In the Harry Potter series, a horcrux is a receptacle in which evil characters store fragments of their souls to enable them to achieve immortality.
Hayashi responded that Abe was only paying his respects to war dead and said his visit was "by no means to pay homage to war criminals or to praise militarism".
"It is ironic that a country that has increased its own military spending by more than 10 per cent a year for the past 20 years should call a neighbour 'militarist'," Hayashi wrote.