The story picks up four years after the events of Mahou Shoujo Lyrical Nanoha StrikerS, in which magical girl Nanoha Takamachi saved and adopted Vivio, the reincarnation of the Sankt Kaiser, Olivie Segbrecht. Vivio is granted her own intelligence gadget, Sacred Heart, after entering her fourth year of primary school, and obtains the ability to shift into her adult Sankt Kaiser mode. She soon meets Einhart Stratos, who, like Vivio, is a descendant of another Sankt Kaiser monarch, Claus G.S. Ingvalt. As Einhart grows motivated to show that her fighting technique is the best, Vivio befriends her and, together with her companions, enters a martial arts competition in which they compete against various supernatural opponents.