Age Maniax ~Isumi Yon Shimai Saigo no Hi~

One day protagonist meets with four sisters, who due to certain events starts living in his house. But he has to go to Europe to follow a story, and they decide to go together with him. They make reservations in an old castle which had reports of a princess' ghost, a legendary wolf, a lake monster and a crashed UFO surrounding it. And this is not even the beginning of the events to unfold around the sisters ...

[Translated From Getchu]

A crossover between multiple age works released in 2000.