Lu over the wall (movie) DVD

Middle schooler Kai moves with his father from Tokyo to the declining fishing town of Hinashi to live with his grandfather following his parents' divorce. Kai finds little to look forward to besides composing music and sharing it on the Internet. One day his classmates Kunio and Yūho invite him to join their band, and when he reluctantly accompanies them to practice on Mermaid Island, the three of them meet a mermaid named Lu.