After a school ceremony, Bobby, an American boy, chooses to head to the mountains with his friend Akkun. They aim to find a perfect spot outside the village to create their secret base. However, on their way, they come across a mysterious amusement park where they get stuck after being attacked. They connect with other lost children and fend off a series of attacks. As they navigate the area, they uncover the truth about the facility. It was created by Koike to ensnare passing children, and his son Takashi requires human children to survive. In an unfortunate turn of events, Akkun is killed, and Bobby gets trapped with a girl named Tokiko. She disappears, and Koike puts Bobby in captivity with the intention of fattening him up. Despite Koike's relentless efforts, Bobby manages to escape. With the support of Saruyoshi, an old hermit who remains a mystery, and the help of the animals in the area, Bobby regains his strength to return to the facility. His goal is to rescue Tokiko from Koike's grip.