MAGICAL GIRL LYRICAL NANOHA VIVID

The manga takes place four years after the JS incident in Magical Girl Lyrical Nanoha StrikerS, and stars Vivio Takamichi, a fourth-year elementary student at St. Hilde Academy of Magic. Vivio has learned to conjure her adult form and has received her own Device, named Sacred Heart, from Nanoha, and has promised Nanoha to never use either for mischief. Then a mysterious magical fighter appears and targets Vivio.