The story is set in Edo period, where male population is decreased to 25 percent of that of female due to a mysterious disease. Because of that, women do all the manual labor and take over businesses while men are treated like essential beings for procreation. Mizuno Unoshin (Kazunari Ninomiya), a young man who pursues the samurai spirit even in this parallel world, decides to sell himself into the harem in the Edo castle (Ooku) to support his family and forget his love with the childhood sweetheart.