Yu Yu Hakusho

Fuutarou Uesugi is a poor, antisocial ace student who one day meets the rich transfer student Itsuki Nakano. They argue but when Uesugi realizes he is to be her tutor, he tries to get on better terms. While trying to do so he meets four other girls.

Before eradicating humankind from the world, the gods give them one last chance to prove themselves worthy of survival. Let the Ragnarok battles begin.

In an alternate history where the male population is nearly decimated, eligible men serve as concubines to the woman shogun inside the walls of the Ooku.