Соответствующая норма
Practice Relating to Rule 135. Children
Japan’s Juvenile Law (1948), as amended in 2010, states: “In the case where a person who is under 18 years of age at the time of his commission of an offence is to be punished with the death penalty, life imprisonment shall be imposed.” 
Japan, Juvenile Law, 1948, as amended in 2010, Article 51. (For a translation of Article 51, see Japan’s initial report to the Committee Against Torture, UN Doc. CAT/C/JPN/1, 21 March 2007, submitted 20 December 2005, Annex XIV, p. 101.)