Third‑grade student Takamachi Nanoha discovers an injured talking ferret that calls out for help. The ferret, Yuuno, is an archaeologist and mage from another world who has accidentally scattered dangerous Jewel Seeds across Earth. Unable to gather the seeds himself, Yuuno has taken on a ferret form and needs someone else to help. He gives Nanoha a red jewel, explaining that it will allow her to transform and use magic to battle the monsters spawned by the Jewel Seeds. However, Yuuno and Nanoha are not the only ones seeking the seeds, and the stakes become far greater than the monsters alone.