Recently the Yomiuri News reported the following:
It was clarified in the whistle-blowing site "WikiLeaks" which opened up diplomatic official telegrams of the State Department one by one, that China had been telling the United States its strong objection over giving a permanent UN Security Council membership to Japan.
According to the same site, last April, China Foreign Secretary's official related a message to people who had ties with US. embassy in Beijing saying that if doubling the permanent membership of U.N. Security Council to ten countries, Sino-U.S. relationship would "Become a troublesome thing", and told that "It is difficult for the Chinese people to accept Japan as a permanent member". The person who had ties with the U.S. embassy answered that "It is not easy to think of an expansion which Japan as the 2nd place donor country of the United Nations budget was not included".
Moreover, Chinese officials said to the people in Beijing who were related to the U.S. embassy last June that "Japan was attaching too much importance to the abduction issue caused by North Korea and that had a force of messing up things instead of being a force for solving problems". In addition, in the opened up official telegrams, in April last year, China Foreign Secretary's officials remarked that "Regarding North Korea it always hoped for a direct negotiation with the United States and tried to draw attention of "adults" (the United States etc.) like a spoiled child." It looked as if China was unable to manage North Korea.
The hearsay is interesting but not unfamiliar. I am wondering if China could give a better reason for rejecting Japan to become a member of the UN Security Council.