Pandora no Yume

The story starts on a summer holiday training camp for members of the arts club. As they are exploring the basement of the European-styled school building, they find a nursing robot called Suu, albeit non functional due to a used-up battery. After being brought back to life by the main character, Hirano Yuito, the robot, of female appearance, recognizes him as her new master.

On the final day, the protagonist prepares to leave after spending an enjoyable week. An earthquake occurs, but he dismisses it as a casual event.
However, before Yuito knows what's happening, all of them are warped back to a week earlier, memories altogether.

As the pattern keeps looping, Suu seems to remember faint traces of the week period, and uncannily starts depicting traits of humanity.