Through the power of a mysterious birthstone, a girl named Miyu can transform into a beautiful and capable detective named Yumi. As Yumi, she works alongside her partner, Takara, solving various cases. However, her feelings for Takara complicate the situation, creating a romantic tension that runs through each investigation. The story blends detective work with romantic comedy, as Miyu navigates her dual identity and her growing attachment to her partner. The manga unfolds across three volumes, with each arc typically centering on a new mystery that tests Yumi's detective skills while also exploring the evolving relationship between the two leads. The birthstone itself remains a central enigma, its origins and full capabilities slowly revealed as the narrative progresses.