One day, Fuyumi receives a stone carving that strikingly resembles Keroro, triggering a mystery that the Keroro Squad must solve. To do so, they venture out to the secluded and enigmatic Easter Island, where they encounter the benevolent Mana spirits, the peculiar twins Io and Rana, and the infamous Akuaku, a malevolent entity that has just emerged from a prolonged slumber.