Соответствующая норма
Japan
Practice Relating to Rule 161. International Cooperation in Criminal Proceedings
Section C. Extradition of own nationals
Japan’s Law on Extradition (1953), as amended in 2004, states:
A fugitive shall not be surrendered in any of the following circumstances … [unless] the treaty of extradition provides otherwise:
(9) When the fugitive is a Japanese national. 
Japan, Law on Extradition, 1953, as amended in 2004, Article 2.1(9).