Kono Yo no Hate de Koi wo Utau Shoujo Yu-No

Takuya Arima is a young student whose father, a famous historian and teacher, mysteriously disappears. Some time later he receives a parcel from his father containing a Reflector device and instructions on how to use it. The device would allow Takuya to travel to parallel worlds. At first he doesn't take it seriously, but soon realizes that the device works indeed, effectively allowing him to experiment different alternative realities and travel between them.