Oooku

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.

(Source: VIZ Media)

Note: The first episode has a runtime of 1 hour and 18 minutes.