Makaeru, a wizard prince of the Land of Frogs and older brother to Princess Mimori, ruled the frog kingdom alongside her after their parents vanished during a historical war between the frog and snake clans. This conflict resulted in both royal families being absorbed into a tunnel. To provide a companion for his sister, Makaeru cursed a human boy named Aoi, causing him to transform into a frog upon water contact, only reverting when completely dry. He instructed Aoi to seek out Mimori in the Land of Frogs to lift this curse.

Before vanishing himself, Makaeru entrusted Mimori with the vital Book of Magic, essential for the frog people's magic. He revealed the book had missing pages and tasked her with their recovery. His disappearance coincided with the loss of the specific pages containing the curse reversal spell, directly triggering the quest undertaken by Mimori and Aoi. Makaeru later reappears, engaging in a magical confrontation. His actions and the mystery of the missing pages drive the core plot focused on undoing Aoi's curse and restoring the lost magic, including the powers the frog king and queen used to seal away the snake clan.