Upon his arrival, Seiichi discovers the island’s unique biological anomaly: for centuries, the women of the island have possessed the ability to carry a fetus to term in just seven weeks rather than the typical nine months. However, a recent decline in genetic diversity among the local male population has caused a reproductive crisis. As an outsider with "fresh" genes, Seiichi is recruited by the island's head to serve as a vital contributor to the island's future.
Each in-game week (7 days), the player must to the female characters ( Mesutachi ) on Koumijima. Failure to fill the weekly quota resets progress or triggers a penalty (narrative or mechanical). Koumijima Shuu 7 de Umeru Mesutachi