Ōoku: The Inner Chambers is a Japanese manga series written and illustrated by Fumi Yoshinaga. It was serialized in Hakusensha's manga magazine Melody from June 2004 to December 2020, with its chapters collected in 19 tankōbon volumes. The manga is licensed in North America by Viz Media. NETFLIX  MADE AN ANIME SERIES OF THE MANGA. 

In Edo period Japan (1603 to 1868), a strange new disease called the Redface Pox has begun to prey on the country's men. Within eighty years of the first outbreak, the male population has fallen to a quarter of the total female population. Women have taken on all the roles traditionally granted to men, even that of the Shogun. The men, precious providers of life, are carefully protected and the most beautiful of the men are sent to serve in the Shogun's Inner Chambers.
This show was really unique—definitely not your average anime. If you are into Japanese culture and traditions, you'll like this show. If you are looking for your classic Isekai, sorry, this is probably not the right show for you
This story takes place in the Edo period where gender roles are reversed and women outnumber men 4 to 1 due to a deadly pandemic called the Redface Pox which only affects young men. Within 80 years one fourth of the men’s population is wiped out, women essentially run the country and men have no choice but to sell themselves in order to be able to make a living. Traditional families are a thing of the past and marriage is considered a luxury only the rich can hope to partake in. The story mainly focuses on the female shogun of Edo castle and the lives of the hundreds of men within it’s inner chamber