i feel like the girl is in a coma, probably from an accident that killed everyone in her family except for her. Because it would be too cruel for her to wake up and face the truth of her family's death, she continues to stay in this place instead, never waking. Coffee seems to be the trigger, as long as she stays in quatre and drinks hakuro's coffee frequently, she wont wake up, kinda ironic imo, and reminds me of how coffee was used in blood-c as well.