Koharu Maezono, who has been deceived and tired of love, returns home, but her father fell ill and the coffee shop he runs was closed without paying back his debt. However, in front of Koharu who wants to protect the shop, a mysterious man named Ryunosuke Date appears. Ryunosuke asked Koharu to marry him instead of taking over her debt, but he already has two wives!? Her hometown, Kita Tsubame City, was the only special zone in Japan where polygamy (Harem Marriage, commonly known as HareKon) was approved as a measure against the declining birthrate and aging population and depopulation. Koharu, who dreamed of marrying her loved one someday, decides to become Ryunosuke's "third wife" in order to protect her store. In this way, Ryunosuke, "the first wife" Yuzu, "the second wife" Madoka and Koharu started a crazy marriage.