Seishun For-get!

From FairGame: "Live with Sincerity" is Natsuki Taiyou's motto. It's the first day of high school, Taiyou was heading to school and then he meets Hinata during the way there. He fell in love at first sight and suddenly confessed to her. Her answer was yes but then she ran away without saying who she was, but it turns out that she was his classmate. Taiyou felt a destiny between them. However, on the next day, she doesn't remember who he is. Why could that be...?