Based on the erotic game by TinkerBell.

Kotone Takashina, Mami Yuzuki, and Yuuri Kanou are three high-school students members of the Mystery Club of their school looking for spooky events happening around. One day, after reading through Internet, a ruined place located in a forest near of their town, Kotone decided to check it and brought her friends with her. However, a sudden downpour took the three girls by surprise and instead of the excepted ruins, they discovered a European-styled mansion whose owners are a mysterious young man and his young twin sisters. The man, Shuuya Houjou, allows them to stay inside of his house until the downpour finishes, but the three girls will soon learn about the dreadful secret hidden inside of the mansion...

(Source: VNDB)