From Aerandria Scans:

The spring when Minori passed her middle-school entrance exams, her granny called her to her atelier and drew a good-luck charm on Minori's back to protect her. But then, her granny passed away without telling her from what she had to be protected from. She only said that when Minori enters high-school she must never ever enter the art-gallery at night. But now Minori is in the art-club. Will she be able to stay away from the Art Gallery as she promised?