Indeed. No way China would accept Japan as a member of the UNSC. Apparently, China is ready to support India's bid for a permanent seat on United Nations Security Council if India did not associate its bid with Japan.however Japan having such power would probably cause many angry nations such as mine.
That said, the support of UNSC P5 member states isn't the only problem. Whether it is Brazil, Germany, India or Japan, or anyone else, the Coffee Club is also another problem... Some of them exert great influence in the UN and are definitely able to convince at least one of the P5 to block the proposal.