Sapphism no Gensou

Story takes place on a fanciful, all-girl educational institution that floats along the oceans. Despite the complete absence of men, there have been incidents of rape amongst the passengers and crew. No one knows who it is just yet, but there are three candidates that carry the high probability of being the next target. Suspense and mystery await as the women suspect one another to be the perpetrator, and who will be next victim. You play as an idol--a female--of the student body who joins in the hunt for finding who did it. The rub lies in the fact that the ship will disembark in three weeks, and the culprit will have gotten away with it by then.

[From White Masq]