Age of consent in Japan is actually kinda blurry. You can't have sex with anyone under 13 period, and people nationwide can if older if they can prove there is a sincere romantic relationship, and parental permission. But individual districts have their own laws, and IIRC no district sets the age any lower than 16 to start, and some are as high as 18, unless they again can prove sincere romantic interest and parental consent, and even then the age range varies. There are also no Romeo and Juliet laws in Japan. Weirdly in Tokyo marriage age is 20 unless you get parents permission, which lowers it to 16 for girls and 18 for boys.