Masuda's characters are in high school and are living in rural areas.
Popee scored an average of 80 points in the graduation exam but for some reason, isn't graduating. Palvan has been a senior for 8 years and Stain has been a senior for 12 years. Why aren't any of the students here graduating?
Whenever you'd ask Papi, the father of Popee and the principal of the school they attend, you'd be ignored and he will not answer. However, he simply just instructs you to "help with field work".
Although Popee hasn't graduated he has nothing else to do in school and has now been farming for 10 months.
And the village, called Masuda Village, was a Genkai shūraku*. The rule "No one is to graduate high school" is a tactic to prevent young people from leaving the village. Radio waves don't even reach smartphones in the village, so there is no wifi. The village was also removed off of Google maps, but no one knows that.
* Genkai shūraku is any village in Japan that has experienced depopulation and in danger of disappearing altogether, largely because more than half of the people living in the village are over the age of 65. Such villages are generally found in mountain villages and outlying islands.
-Wikipedia
Boys who are supposed to be adults are trapped here without knowing they are capable in society. How long will a child be a child, and when will he become an adult? How will the souls of these men continue to remain as children?
Their youth will soon be drawn from them.