Nana Suzuki is a middle-schooler with a huge crush on a boy named Yuuichi, with whom she shares a class.

One day, she tries to bake a cake for her crush for Valentine's Day, to discover that the microwave is in the shed--being used in an experiment crafted by her grandfather. Inside, she discovers a heart-shaped prism which shoots out in seven different colors and splits her into seven Nanas!