Appearing as the main obstacle for the characters in both the Kemono Friends game and the Kemono Friends anime, Cerulean were first formed after the First Eruption on Japari Island. The outbreak forced Japari Park to close and have all the island's humans evacuated. Though the park was eventually cleaned out from the Cerulean threat, the Second Eruption caused a larger outbreak that led the park having become a danger to everyone living on the island once again. The park was closed and the efforts by Mirai to save and reopen the park once again failed.