Switching - Goodbye Me (2007)

Original title: 転校生 -さよなら あなた-

After his parent's divorce, Kazuo Saito moves with his mother from Onomichi and must leave his girlfriend behind. At his new school, Kazuo is surprised to reunite with his childhood friend Kazumi. After talking about old times, they walk to a place from their childhood called the “Lonely Watering Place” but the two accidentally fall into the water. They quickly crawl out, but suddenly realize that they have switched bodies!