The Democratic Party of Japan may have obtained a powerful weapon Tuesday to wield against Prime Minister Junichiro Koizumi: former Foreign Minister Makiko Tanaka.

Tanaka, an extremely popular political figure among female voters and one of Koizumi's most vocal critics, joined a 179-member Diet group comprising 177 DPJ members and two independent lawmakers just one day before a special Diet session is set to convene.

While Tanaka will not be a DPJ member, she will now have opportunities to speak at Diet sessions within the question time allocated to the largest opposition party -- and possibly to grill Prime Minister Koizumi.