Prizona 6

Longitude unknown
Latitude unknown
This island has no name.
Everyone just calls it Island.

Seven girls who have no memory of their past or even their name lives on this island. Both the town and island are deserted but water and food are supplied to them each month. The girls call each other by numbers and names associated with the number. Number 6, Mutsuka is a girl desperately trying to get back to her beloved sempai. She has tried 16 times but she won't give up until she succeed. In her attempts she'll learn about the other inhabitants and about the island and not all of it are pleasant.