Switching Goodbye Me, Sayonara anata, 転校生 さよなら あなた (2007) dir. Nobuhiko Obayashi

After his parent s divorce, Kazuo Saito moves back to his hometown of Nagano with his mother. He leaves behind his girlfriend. At his new school, Kazuo Saito meets his childhood friend Kazumi Saito. Although Kazumi Saito has a boyfriend, she is comfortable hanging out with Kazuo Saito. They decide to visit a spring that they frequented as kids. While at the spring, Kazuo and Kazumi fall into the water. They quickly get out of the spring, but their bodies have switched