It is currently the Taiheimeji Era. It is a reign ruled by the Tokugawa shogunate. Inside this shogunate, there is a group of warriors that support the government. They are the Manyuu Clan.

In this current era, breasts mean everything. If you have breasts, you are guaranteed wealth and popularity. If you lack them, you are rarely considered “human”. Members of the Manyuu Clan help raise the future big breasts. Written on a secret scroll possessed by the clan, there is said to be various techniques on how to grow big and beautiful breasts.

Chifusa is to be successor of the clan. However, she takes the secret scroll and runs away with it, hoping to fight against the cruel world that the Manyuu Clan has created…

[Source: MyAnimeList]