Japan has entered a society with a seriously declining population.
The "Ikumono-gakari Law," enacted as a countermeasure to the declining birthrate, makes sexual intercourse obligatory, and boys and girls learn sexual acts at school.
However, the young boys and girls are so excited by the sex acts, even though they are in class, that they gradually escalate the situation...
They let their sexual desires take over, and the orgy begins!