LOL, Japan's entry to the UNSC is opposed by China, Russia and South Korea. Two veto members.
The chances of any grouping that includes Japan getting permanent seats is non-existant.
Nothing personal against them, it is just that Japan will echo the USA's line, and that would put the entire UNSC in America's pocket, even more than it already is.
I think the better answer on this Japan thing was the one you gave to liquid in post#57.
Anyways don't you think though japs don't have a strong military but they have a strong economy and it plays a major role too and Japan at current time is one of the most peacefull nation they should be allowed for atleast the decision making part .