Manaka Junpei encounters a beautiful girl on the roof of his school. Pictured against the backdrop of the setting sun, with her wind blowing through her hair, Junpei manages to catch a glimpse of her strawberry panties. Embarassed, the girl runs away before he even gets the chance to talk to her. His only clue is the math notebook she dropped, with the name 'Toujou Aya' written on the cover.

The next day, he finds that the 'Toujou Aya' who owns the notebook is the exact opposite of the girl he saw on the rooftop. There’s no way it can be her, can it?