ef: A Tale of Melodies.

Synopsis

A flashback is shown with Yu Himura, Yuko Amamiya, and Shuichi Kuze in their younger days as high school students. At this time, Yu and Yuko have not seen each other for ten years. In the present day, Mizuki Hayama is staying over at Renji Aso's house for the time being until she enters high school, not having much to do while Renji studies for exams. Sumire Aso introduces Shuichi to Mizuki, who discovers some of the things Renji was trying to warn her about him might be true. Kuze and Mizuki spend the rest of the day together, and the two become more familiar with each other.

(Source: Wikipedia)