Long ago, there was a world where magic and science coexisted. Fearing what humans might become, God split that world into two separate realms: Elde, a land of advanced science, and Fandavale, a realm rich in magic. In Fandavale, a wicked witch named Cendrillon rises, aiming to conquer both worlds. To accomplish this, she seeks the "key"—a source of immense power.
In Elde, a young boy named Sōta meets a peculiar girl from Fandavale, Akazukin, along with her talking wolf companion, Val. Sōta learns that he himself is the key that Cendrillon desires. With that revelation, Akazukin, Val, and the other Fairy Musketeers set out to protect Sōta from Cendrillon and her Nightmarelians, who are determined to seize the power he holds.