Japan did not sign the RS before the closing date for signature, December 31, 2000, mainly because it was deemed difficult to review all the legal obligations in the treaty and thus determine whether necessary domestic legislation could be prepared in a timely manner. 
Japan’s observation: states practice shows that when it comes to ratification or accession to the RS, states have taken at least two possible approaches…the first one is to amend existing criminal laws and other relevant domestic legislations such as Denmark and Canada as well as France with regard to the areas of extradition and mutual assistance; Canada has introduced Crimes Against Humanity and the War Crimes Act for punishing crimes under the RS, while amending the existing Extradition Act and Mutual Legal Assistance Act; while France amended its law on criminal procedure and is currently in the process of reviewing its penal code (2005)…the second approach is to devise an entirely new comprehensive legislation for securing obligations under the RS, such as UK, Germany and NL. 
The principle of complementarity has merits from a political viewpoint. On the part of states, there was strong hesitancy about conceding its sovereign rights to an international organization. This is one of the main reason why the international community has not been successful in creating a permanent ICC over a half of century. Both preserving national jurisdiction and enabling the Court to intervene under certain conditions, the complementarity principle accommodates a very delicate balance between state sovereignty and the integrity of the court.