On January 20 , 2006 , Prime Minister Junichiro Koizumi made an announcement that they would change the law to allow women to ascend the throne . On January 20 , 2006 , Prime Minister Junichiro Koizumi devoted part of his annual keynote speech to the controversy , pledging to submit a bill allowing women to ascend the throne to ensure that the succession continues in the future in a stable manner .