If they're in their last year of middle school in Japan they're probably about 14-15 years old, which is also the age range of first years in high school in some other countries.... where undoubtedly most kids start hitting puberty and engaging in sexual activities. And I wouldn't call it "porn". It's just a romance story with a mature rating if anything. Just because something has sex in it doesn't mean it's supposed to be porn or used for the same thing as porn.
Too late
There's no legal age of consent in Pakistan ( ° ʖ °)
Okay...ummm...I thought they sere 17-18, not 14!!! Eww!! I do not want to read porn about kids!!!