The Age of Consent for Japan, across the board, is 18 if you're an adult.
It's a popular myth that perverted weeaboos have promoted that Japan has an age of consent as low as 13 in some prefectures, and therefore it's free real estate to fuck Japanese girls, but no. If she's 14, then in some prefectures it'd be okay for another 14 year old boy to fuck her, other prefectures say she's not able to consent until she's 16, but if you're a grown ass man trying to fuck her, you're going straight to prison regardless of her age until she's 18.
Those laws don't exist to allow foreigners to take advantage of young Japanese girls, they exist so Japanese teenagers who get horny won't become criminals just for doing what teenagers do when they start noticing the opposite sex looks good.