Kouji Harada is an elementary school student who wears glasses and possesses a strong, insatiable curiosity for unconventional subjects. His interests fixate on UFOs, aliens, and the occult, earning him a reputation as the bookworm among his peers.

On his journey, Kouji encounters an alien named Ink, a traveling repairman who works with her father, Rubin. This meeting sparks a friendship between them. Rubin owns a rocket ship, a project built painstakingly over time from spare parts. This very rocket later enables the children to travel to the Pet Star for an interstellar festival, where they confront the primary antagonist.

Kouji’s actions are propelled by his inquisitive spirit and fervent enthusiasm for the unknown, traits that define his character. His bond with Ink serves as his personal gateway into the wider alien community explored throughout the adventure.