In the wilderness of Hokkaido, the Ainu people of Japan live in harmony with nature. Kotan Nakamura is a young Ainu boy living peacefully until he meets a tiger one day. This tiger, Dan, has escaped from a train that was carrying him to a zoo. Together, they discover mysterious ruins hidden underneath the ground.

Within the ruins, Kotan and Dan discover an old man named Upopo living there. He tells the boy and the tiger about three keys to a fantastic treasure. As it so happens, the evil Sekkoku Kou is also searching for the treasure and shoots Upopo. Before he dies, Upopo gives one of the keys to Kotan.

Now, Kotan and Dan find themselves involved in an ugly battle as numerous villains track them down to try to get the three keys so they can claim the treasure.