Japan has plunged into a society with a serious population decline. The Ikumonogakari Law, which was enacted as a countermeasure against the declining birthrate, made sexual intercourse compulsory, and boys and girls learned sexual intercourse at school. However, even though it is a class, they are very excited about naughty acts, and they gradually escalate-- To the all-you-can-eat big orgy that you want to leave to libido!