Manami no Doko made Iku no?

Manami was just about to begin enjoying her summer vacation, when she received a strange letter. The sender implies that Manami has been chosen as a heroine, and her task is to stop a criminal syndicate in her home town. As the girl begins investigating nearby areas, she meets a mysterious masked person known as Black Pack, and delves deeper into conspiracies and bizarre sexual encounters.

[From Moby Games]