Tokyo has become a society where magical girls, once mere fantasy, now actively operate in reality due to the emergence of the mysterious lifeform known as the Black Calamity. Yumeri Hanasaki, a 30-year-old single office worker, has only one hobby: being a magical girl otaku. Though she finds herself drawn to her colleague Sota, who often chats with her in a friendly manner, she keeps her feelings hidden, convinced someone like her could never be his match, and lives an ordinary, unremarkable life. One day, Yumeri witnesses Sota being attacked by a Kuroka. There, a mysterious young knight named Mira appears, claiming to be a fairy from another world. At her request, Yumeri makes a contract to become a magical girl to save Sota. But after transforming, she finds herself as a beautiful 15-year-old girl embodying her ideal self—!? A lyrical work story for girls who never quite grew up.