Doukoku Soshite...

In this game, you play the role of a high-school student (whom you can name as you like). A bus takes him and his classmates to the school every day. But this time, just when the hero was talking to one of his classmates, the lovely girl Riyo, a car drove up to the bus, there was a sound of a crash, and then the hero became unconscious. When he woke up, he found himself, his classmates (most of whom were girls), and a couple of unknown people in a locked room in a strange mansion. Soon the hero realizes something terrible is going on in the mansion. People are being killed under mysterious circumstances, their corpses hidden; he finds a memo soaked in blood and a photograph. Will he be able to solve the mystery and to protect the people destiny brought him together with?

[From MobyGames]