Asia's two biggest economies both have their most powerful leaders in decades — and neither one has much incentive to mend a relationship that has long been volatile.

Polls show Prime Minister Shinzo Abe's ruling party is heading for a landslide win in Sunday's election, putting him on track to become the longest-serving leader in the country's history. Similarly, President Xi Jinping may enter his second term next week as China's strongest leader in at least a generation.

When both men rose to power in 2012, ties were at the lowest point since the nations agreed to establish diplomatic ties in the early 1970s. Fears of a military clash swirled as ships and planes from both countries tailed one another around disputed islands known as the Senkakus in Japan and Diaoyus in China. Anti-Japanese demonstrations in China hurt trade and investment.