Jiro Matsuzawa is an ordinary elementary school boy. One night, an old man comes in with a trunk, containing two smaller trunks. The old man presents one to Jiro, and Jiro is permitted to have Burunga take on whatever form he wishes him to.

Jiro finds Burunga to be a bit of a handful, but with the help of Taro Katagiri, a young ruffian who has his own agenda for Burunga, he manages to keep Burunga under control. However, Burunga's purpose, as well as the identity of that old man, are more sinister than Jiro could have expected...