Ryusuke is a junior high school student living in Tokyo. During his summer vacation, he visits Tokushima and reunites with his teenage cousin, Tomomi. Ryusuke and Tomomi go outing to the Anabuki River where they get swept away by the rushing current. As they sink to the bottom of the river, a dragon appears, rescues them, and takes them to a mysterious old man. The old man tells Ryusuke and Tomomi that they are alrea...