Ao Haru Ride.

At the end of the first year of high school, Futaba Yoshioka meets Kou Tanaka who was her first love. In their middle school days, they attended the same school, but he suddenly transferred to another school. Three years later, he appears in front of her again with the different last name of Kou Mabuchi. His personality also seems to have changed from warm to cold. He is like a totally different person from three years ago. Futaba Yoshioka slowly learns what happened to Kou Mabuchi for the past three years and she become to have feelings for him again.