The hero has defeated the Demon Lord and peace has returned to the land, but some day in the distant future, the Demon Lord will return. In order to ensure that the hero's bloodline will remain to defeat him once again, women from across the world have been gathered to form a harem and bear his children.
The series follows the various (and often incredibly lewd) conversations the members of the harem have to kill time as they wait for their turn with the hero, and for their children to be born afterwards.