The Hague Convention on International Child Abduction is an international treaty which:

1) supports the prompt return of wrongly removed or retained children, and

2) calls for all participating parties to respect parental custody rights

The Convention of 25 October 1980 on the Civil Aspects of International Child Abduction (HCCH 1980 Child Abduction Convention) is a multilateral treaty, which seeks to protect children from the harmful effects of wrongful removal and retention across international boundaries by providing a procedure to bring about their prompt return and ensuring the protection of rights of access. The "Child Abduction Section" provides information about the operation of the Convention and the work of the Hague Conference in monitoring its implementation and promoting international co-operation in the area of child abduction. 

Japan became signatory to the Hague Convention on International Child Abduction in April 2014

Today, the US Senate has identified Japan (among other countries) as engaging in a pattern of noncompliance to this treaty.

https://www.congress.gov/bill/117th-congress/senate-resolution/568/text/rs?r=2