ChronoBox

Nayuta was one of many students who attended “EDEN” on a small solitary island called “Angel Island”. The enjoyable time that he spent together with his friends was put to an end by a sole black box and a “girl in black”.

Surely, it will be all right. It’s best to keep forgetting the past which should not be remembered and continuing living their lives with their angel-like friends who have gathered in EDEN. The nightmare on which the girl leads them has yet to end...

[From Hau~ Omochikaeri!]

Beware that the three trials have exclusive content. The first trial is a prequel to the game, the second one includes Kokuchounuma Shie's route, and the third one includes Kanami Niwaka's route.
Those trials can be integrated to the main game (accessible in the EXTRA menu) through a special installer.