The proper venue for Japanese security concerns by treaty is the South East Asia Treaty Organization (SEATO).
Unfortunately, SEATO has been dissolved as the United States was driven from all the member states except Australia, New Zealand, and those South Pacific states the United Kingdom and France.
This is clearly an attempt to proxy Japan into conflict with China and Russia.
Japan is unable to oppose either or settle their legitimate problem with North Korea without considerable military backing from the United States.
Noting that the US has already effectively abandoned Taiwan to China, and Japan to North Korea when they could have easily backed both, the Japanese should seriously consider the real intentions of the proposal, and the United States Obama Regime, before signing on.
The "successor" to NATO will include the five Anglosphere nations only, if the US stays together and can manage it.