International Criminal Law in Japan

Overview of International Criminal Law in Japan

Japan’s relationship with international criminal law occupies a distinctive position in the global legal order. As the first Asian state to ratify the Rome Statute of the International Criminal Court (2007), Japan has positioned itself as a bridge between Western and Asian approaches to international criminal justice. Yet Japan’s domestic implementation of core international crimes remains incomplete, its historical confrontation with wartime responsibility continues to generate controversy, and its constitutional pacifism — codified in Article 9 — constrains the scope of its participation in international peace operations. This article examines the three principal dimensions of international criminal law in Japan: (i) Japan and the International Criminal Court (ICC); (ii) Japan’s domestic legal framework for international crimes; and (iii) the legacy of the Tokyo Trials and the unresolved questions of historical justice.

Japan and the International Criminal Court

Japan signed the Rome Statute on 7 October 1998 and ratified it on 17 July 2007, becoming the 87th state party and the first — and, as of 2026, still the only — Asian member of the Group of Western European and Other States (WEOG) within the Assembly of States Parties. The ratification followed years of parliamentary deliberation, during which concerns about constitutional compatibility — particularly regarding the surrender of Japanese nationals to a foreign court — were resolved through the enactment of the Act on Cooperation with the International Criminal Court (Kokusai Keiji Saibansho e no Kyoryoku ni Kansuru Horitsu, Act No. 37 of 2007; “ICC Cooperation Act”).

The ICC Cooperation Act provides a comprehensive framework for Japan’s compliance with Part 9 of the Rome Statute (international cooperation and judicial assistance). It authorizes the surrender of persons (Articles 23–40), including Japanese nationals, to the ICC — the constitutionality of which was affirmed by the government on the ground that Article 9-2 of the Constitution permits the surrender of nationals to international courts established by treaty. The Act also provides for the gathering of evidence, the enforcement of ICC fines and forfeiture orders, and the enforcement of ICC sentences of imprisonment in Japanese prisons (though this last provision has never been activated). The Ministry of Foreign Affairs serves as the central authority for cooperation requests.

Japan is the ICC’s second-largest financial contributor (after Germany), providing approximately 16% of the Court’s budget in 2025. Japanese nationals have served as ICC judges, including Judge Kuniko Ozaki (elected in 2017, formerly a diplomat and legal adviser to the Ministry of Foreign Affairs) and Judge Tomoko Akane (elected in 2018, formerly a prosecutor and member of the UN Committee against Torture). Judge Akane served as the ICC’s First Vice-President from 2021 to 2024. Japan has also seconded prosecutors and investigators to the ICC’s Office of the Prosecutor and has contributed financially to the Trust Fund for Victims.

Domestic Implementation of Core International Crimes

Japan has not enacted comprehensive implementing legislation defining genocide, crimes against humanity, or war crimes as separate domestic criminal offences. Instead, the government maintains that existing provisions of the Penal Code (Keiho) — including the offences of homicide (Article 199), assault causing death (Article 205), unlawful confinement (Articles 220–221), and arson (Articles 108–110), among others — are sufficient to prosecute acts that would constitute core international crimes. This approach has attracted scholarly criticism on three grounds.

First, the ordinary domestic offences fail to capture the contextual elements of international crimes — the requirement under the Rome Statute that genocide be committed with intent to destroy a national, ethnical, racial, or religious group (Article 6), and that crimes against humanity be committed as part of a widespread or systematic attack directed against a civilian population (Article 7). Japanese courts have no statutory basis for applying these contextual elements, meaning that a perpetrator of genocidal killings could be prosecuted only for individual homicides, without the stigma or gravity of the international crime. Second, the Penal Code does not recognize command responsibility (Rome Statute Article 28) as a distinct mode of liability. A military commander who knew or should have known that subordinates were committing atrocities but failed to prevent or punish them would be prosecutable only through ordinary aiding and abetting principles, which require proof of affirmative assistance — a higher evidentiary threshold. Third, the Penal Code’s statute of limitations (which was abolished for murder only in 2010 but still applies to other serious offences) would bar prosecution for many war crimes committed more than 15 years ago.

The consequence is that Japan lacks the legal capacity to prosecute core international crimes in their international legal character. This gap has practical implications: if Japanese nationals serving in UN peacekeeping operations were accused of war crimes, or if the Security Council were to refer a situation involving Japanese nationals to the ICC, Japan would be unable to exercise primary jurisdiction through a domestic prosecution, potentially triggering ICC admissibility proceedings.

The Tokyo Trials and Japan’s Wartime Legacy

The International Military Tribunal for the Far East (IMTFE, the “Tokyo Trials”) sat from 3 May 1946 to 12 November 1948, prosecuting 28 Japanese civilian and military leaders for Class A crimes (crimes against peace, conventional war crimes, and crimes against humanity). The Tribunal was established by a special proclamation of Supreme Commander Douglas MacArthur and functioned under a Charter that substantially replicated the Nuremberg Charter but with notable divergences — including a broader definition of crimes against peace and the absence of a crime of conspiracy. The IMTFE convicted all 25 surviving defendants (two died during proceedings, one was found unfit), sentencing seven to death (including former Prime Minister Hideki Tojo), 16 to life imprisonment, and two to lesser terms.

The Tokyo Trials remain a contested legacy in Japan. Unlike Germany, which has largely integrated the legal and moral judgment of Nuremberg into its national identity, Japan continues to debate the legitimacy of the IMTFE’s jurisdiction, the retroactivity of its charges, and the selectivity of its prosecutions (which excluded the Emperor and failed to prosecute the Unit 731 biological warfare program). The Japanese government has adopted a posture of de facto acknowledgement — accepting the Tokyo verdicts in the 1951 San Francisco Peace Treaty as a condition of sovereignty — while avoiding formal legislative or educational measures that would institutionalize the Tribunal’s historical narrative.

Universal Jurisdiction and the Comfort Women

Japan has not enacted legislation conferring universal jurisdiction over international crimes. The Penal Code is strictly territorial (Article 1), with limited extraterritorial application only for specific offences committed abroad by Japanese nationals (the active personality principle). This means that Japan would not prosecute a foreign national found on its territory who is alleged to have committed genocide or war crimes abroad — a gap that human rights scholars have urged the Diet to fill.

The comfort women system — the systematic sexual slavery of an estimated 50,000 to 200,000 women and girls, primarily Korean but also Chinese, Filipino, and Dutch, by the Imperial Japanese Army during World War II — illustrates the limits of international criminal prosecution for historical atrocities. Although the IMTFE heard some evidence of sexual violence, the Charter did not expressly list sexual slavery as a crime against humanity, and no defendant was convicted on that basis. Subsequent attempts by former comfort women to obtain civil compensation through Japanese courts have been uniformly rejected — most recently in the 2021 Supreme Court decision in Kim v. Japan — on the grounds of sovereign immunity and the 1965 Treaty on Basic Relations between Japan and the Republic of Korea, which the Japanese government interprets as having settled all claims arising from the colonial period. The UN Committee on the Elimination of Discrimination against Women and the Special Rapporteur on violence against women have repeatedly criticized Japan’s failure to provide effective remedies, but international criminal law — with its forward-looking jurisdictio—has proved an imperfect vehicle for addressing these claims.

Japan and UN Peacekeeping Operations

Japan’s participation in UN peacekeeping operations (PKOs) is governed by the International Peace Cooperation Act (Kokusai Heiwa Kyoryoku Ho, Act No. 79 of 1992), enacted after the Gulf War and Japan’s controversial financial contribution without personnel deployment. The Act authorizes the deployment of Japan Self-Defense Forces (JSDF) personnel to PKOs subject to five principles: (i) a ceasefire must be in place; (ii) the parties must consent to the operation; (iii) the operation must be impartial; (iv) Japan may withdraw if any condition is violated; and (v) the use of weapons is limited to self-defence. The Act was amended in 2015 to permit the collective self-defence operations — JSDF personnel may now use force to defend allied forces, not just Japanese nationals — a change that expanded Japan’s potential exposure to the laws of armed conflict.

Conclusion

Japan’s engagement with international criminal law is marked by paradox. It is the leading Asian state within the ICC system, a major financial contributor, and a source of distinguished judicial talent. Yet its domestic law lacks the fundamental apparatus to prosecute genocide, crimes against humanity, or war crimes as distinct offences; its confrontation with the Tokyo Trials and the comfort women system remains incomplete; and the constitutional and political constraints on its peacekeeping role leave it in an ambiguous position between the global North’s assertive universalism and Asian states’ traditional defence of sovereignty. The direction of travel — toward deeper integration with the international criminal justice system — seems clear, but the pace of reform remains subject to the same political dynamics that have shaped Japan’s postwar legal identity: between internationalism and nationalism, between reckoning and amnesia.