Permanent member of the Security Council

Japan seems to want to be a permanent member of the Security
Council... I cannot find the reason why it is necessary, but Japanese
government and/or the Ministry of Foreign Affairs think so. Even the
mass media don't say the convinced reason. Of course, I know that
Japan contributes much money to the UN, but then what?
Today's subject was heavy... I'm not so good at talking about politics
etc. However, the above one is my recent not answered question...