Even as Sino-Japanese ties hit their worst in four decades, relations between Beijing and Seoul have never seemed warmer, which could sway the dynamics in the North-east Asian region, say analysts.
A firm piece of proof lies in news last week of a plan by the two sides to build a statue of a Korean activist who fought against Japanese colonial rule in the Chinese city of Harbin, a move that has irked Japan.
Seoul and Beijing both hold up Ahn Jung Geun as a hero for shooting dead Hirobumi Ito, the Japanese colonial governor of Korea, in Harbin in 1909. Korea was under Japanese rule from 1910 to 1945.
Seoul's response to China's controversial East China Sea Air Defence Identification Zone, which overlaps with South Korea's airspace, has also been milder compared with that of Tokyo and Washington.
Observers also note how the Chinese media had given glowing coverage of South Korean President Park Geun Hye's visit to China in June, praising her command of the Chinese language and publishing her biography.
And Chinese President Xi Jinping agreed to Ms Park's request to speak on the phone about North Korea earlier this year, amid provocative acts by the nuclear-armed country.
A phone chat was something their predecessors, Mr Hu Jintao and Mr Lee Myung Bak, have never done, noted Dr Sunny Lee, a former Beijing-based journalist and now a fellow at Stanford University. He wrote in a paper that such developments reflect a honeymoon phase in Chinese and South Korean ties.
He told The Straits Times the possible reasons.
China sees the Washington-Seoul-Tokyo alliance as a structure set up to contain its rise. "Naturally, China wants to break it, making a hole in the structure. China sees South Korea as fair game," he said.
On the other hand, South Korea thinks it has "a real chance of making Beijing closer to it than it is to Pyongyang" and thus influence China's policy over North Korea, he added.
Then, of course, there is the Japan factor, as pointed out by analyst Tetsuo Kotani of the Japan Institute of International Affairs. "China and South Korea have difficult relations with Japan, so by strengthening their relations, they want to press Japan to make compromises."
Last month, South Korean Ambassador to China Kwon Young Se said his country would work more with China to pressure Japan into making concessions on issues like history and contested territory.
Ironically, South Korea has not previously been as close to China as Japan. While China and Japan normalised ties in 1972, South Korea did not have formal ties with China until 1992.
South Korea's two-way trade with China hit US$256 billion (S$320.7 billion) last year, lower than the US$329 billion in Sino-Japan trade.
While economics used to dominate, Beijing and Seoul are increasing cooperation in other areas.
China State Councillor Yang Jiechi, for instance, met Mr Kim Jang Soo, chief of the Blue House's National Security Office, for the first high-level bilateral security talks during a visit to South Korea last week.
But analysts say there is a limit to how close Beijing and Seoul are likely to become.
Seoul still needs Tokyo's help, said Mr Kotani. "South Koreans should be reminded that they cannot have leverage over the North without Japan's support."
It also cannot do without the United States, said Beijing-based Korean expert Zhang Liangui. "South Korea can't weaken its ties with the US as it needs the US security umbrella to protect its safety."
Analysts agree that Beijing is unlikely to be influenced by Seoul over Pyongyang, one of China's few remaining communist allies.
And when the love affair sours, Seoul will likely be the loser.
"China has little to lose. But South Korea will have to pay handsomely, as a weaker party of the relationship," said Dr Sunny Lee.
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