Mahou Shoujo Lyrical Nanoha ViVid

Four years after the JS Incident, Vivio Takamachi enters the fourth elementary grade at St. Hilde Academy of Magic. She has since learned to conjure her Adult Form at will and received her own Device, Sacred Heart, from Nanoha, who made her promise to never use either of the two for mischief. However, a real danger soon arises in the form of a mysterious magical fighter, Heidi E.S. Ingvalt, who named herself after an Ancient Belkan ruler and now targets both Vivio and Ixpellia... (Source: ANN)