Nangoku Sakunyuu Island

Storyline
The main character drifted to a tropical island without his memories. On the island lived a tribe of huge-breasted girls, who kindly took him in. The economy of the island rests upon human milk. A man known as "One-Shot Expert" regularly sails to the island, extracts milk from the girls, and sells the milk off-island.

However, one day, One-Shot Expert disappeared. Milk production depended on having sperm ejaculated inside the female, and the main character is the only other male on the island. Our hero now has to work hard to repay the girls for their kindness, or the island will be ruined!