On the last day of the school year, 14-year-old Ichika Tachibana is on cleaning duty and gets the daunting task of cleaning a huge mirror. As she cleans, a mysterious girl named Manatsu comes out of the mirror and asks for some homework help... and ends up granting Ichika magical powers for the summer! But these powers come with a price, and both of the girls will learn that before summer's end.