DUNAMIS15

Takatsuki Tougo is leading a boring life at Ceres Academy, located on an isolated island called Dunamis Base. One day, while rushing to class after having overslept, Tougo stumbles upon a mysterious girl in the school hallway. This brief encounter then changes Tougo's life forever.

Time in the game will loop, so the player will end up experiencing the same story repeatedly. The player will need to follow the proper route in order to escape from this loop.

[Edited from Wikipedia]