未熟之夏 (2006)

After becoming obsessed with a 15-year-old schoolgirl (Japanese porn star Sora Aoi), a perpetual loner named Masuo Ota (Yutaka Mishima) finds himself aroused by the slightest provocation. Unable to control his swelling passion, he devotes his life to following her -- everywhere she goes. Will the object of his affection ever return his feelings, or is Masuo destined to be consumed by his twisted desires?
It's the debut film from Keisuke Yoshida.